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I took apart my old radio, I honestly didn't hear an issue with the volume, it must have been "cured" or it's such a long and slow drop I was not able to notice it during the time I listened. I decided to look at the cassette portion instead. Cassette side on bottom  Had to cut two wires to lift it up, they go to the cassette motor.   It seems to use a square belt but it's really slack, so slack it fell off the pulleys. I guess it's an age thing. When you press the play button the center pulley moves inwards and lessens the belt tension even further. Made me wonder if the belt is supposed to run along the inside of that pulley. It moves outwards when using rewind or forward though.  And the other side of the cassette unit  Next step is gonna be plugging it in and see if the power cables delivery any juice to the motor, it does not engage at all.
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Sep 15, 2021 06:03
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Looking for something weird: I need a variable resistor in the range of ~10 - 100 ohms, and would be considered RF compatible (so not wire-wound).
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Sep 15, 2021 21:28
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Cyril Sneer posted:Looking for something weird: I need a variable resistor in the range of ~10 - 100 ohms, and would be considered RF compatible (so not wire-wound). Would either a trimmer pot or slider pot be suitable?
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Sep 15, 2021 21:42
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poeticoddity posted:Would either a trimmer pot or slider pot be suitable? Yep. Actually, this will probably do the trick - https://www.digikey.ca/en/products/detail/tt-electronics-bi/93PR100LF/6155633
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Sep 15, 2021 22:25
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Could someone help me understand what's happening to my circuit? My problem is when I'm trying to charge a battery through wall power, the charger keeps turning off and on about once a second. The intended behavior is that the charger should stay on, delivering current into the battery until full charge and then trickle charge after that. I have a soft power switch from sparkfun hooked up to a battery babysitter that leads to a Raspberry pi and on the other side is a single 18650 cell. The schematic of the power switch is below:  The pin "fast off" is unconnected and the one labeled "sense/ctrl" is hooked up to GPIO 6 of the raspberry pi. This pin is configured as an INPUT when the device is on and then switches to OUTPUT and pulled low when the device shuts down. When it's off, I observe that it's at 0V. When the raspberry pi is on, charging works perfectly fine. When I turn the device off, three unexpected things happen: 1. If the device is off and I plug in power, it will turn on the device. Mostly just a minor annoyance. By look at the schematic, I don't think it's supposed to be doing that. 2. If the device is off and the power is plugged in, the charger will turn on and off about once a second (observed by the LED going on and off). I.e. it's not charging the battery properly. 3. While the device is off and the power is plugged in, I am unable to turn the system on. This might be related to 1) and 2) because when the power is plugged in, the switch appears to be some sort of undefined state and the nodes near the switch are in their "on" voltages. If I disconnect the sense/ctrl pin entirely, the charging works. So I suppose the way I hooked up GPIO 6 might have something to do with the first two issues. Unfortunately, I need this pin to be hooked up so that my system works. Also, I've observed that the voltage of the node going into the gate of the bottom transistor oscillates between ~1V and -4V periodically coinciding with the charger shutting off. Anyway, the bottom line is that Sparkfun claims that it supports charging through the body diode of the top transistor: quote:The Soft Power Switch supports battery charging. If the target device has onboard LiPo charging, current can be passed back through the cut-off circuit and charge the battery. But it doesn't seem to be working for me and I don't know if it's because the claim is false, or if there's an issue with the design, or if I'm just using it wrong because I have no idea what I'm doing and there's barely any documentation to tell me otherwise... Cory Parsnipson fucked around with this message at 03:37 on Sep 16, 2021 |
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Sep 16, 2021 03:34
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Should the battery babysitter be charging the battery through the diode in that PMOS like that? That'll significantly change the measured cell voltage when the power is off. It would make more sense to me if the charger was on J8.
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Sep 16, 2021 04:16
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Stack Machine posted:Should the battery babysitter be charging the battery through the diode in that PMOS like that? That'll significantly change the measured cell voltage when the power is off. It would make more sense to me if the charger was on J8. Ah ok, so that's the way I had it originally. The power switch was between the charger (buck/boost converter, actually) and the Raspberry pi, but then I read this: quote:The Soft Power Switch supports battery charging. If the target device has onboard LiPo charging, current can be passed back through the cut-off circuit and charge the battery. So I thought, huh, maybe they intend for it to be directly in front of the battery instead? I thought this would be convenient because when the device is off, the quiescent current is much lower.
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Sep 16, 2021 04:31
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If I understand correctly, you can still have the battery on J10, the battery babysitter on J8, and the buck/boost to the raspberry pi on J7 and have pretty much your desired setup. The only thing is you probably won't be able to use the battery babysitter through J2 since the raspberry pi holding GPIO 6 low will keep the PMOS turned off and make it behave like a diode with a drop of hundreds of mV instead of a closed switch.
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Sep 16, 2021 04:56
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Stack Machine posted:If I understand correctly, you can still have the battery on J10, the battery babysitter on J8, and the buck/boost to the raspberry pi on J7 and have pretty much your desired setup. The only thing is you probably won't be able to use the battery babysitter through J2 since the raspberry pi holding GPIO 6 low will keep the PMOS turned off and make it behave like a diode with a drop of hundreds of mV instead of a closed switch. Oh that's interesting, hooking up both J10 and J8. Never thought of that since they're tied together. But I'm not sure how to hook the babysitter up to J8. It has a port for the battery and then a separate port for "Vout" that's supposed to go into the device.
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Sep 16, 2021 07:12
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Cory Parsnipson posted:Oh that's interesting, hooking up both J10 and J8. Never thought of that since they're tied together. But I'm not sure how to hook the babysitter up to J8. It has a port for the battery and then a separate port for "Vout" that's supposed to go into the device. Oh, I see. That makes it more difficult since then you're bypassing the switch if you just connect it to J8. You could leave the charger on J2 and try a 220μF capacitor between GPIO 6 on the Pi and sense/ctrl on the switch board. This will charge up within a few seconds and turn the PMOS back on if the charger is charging. I won't guarantee it'll work since the capacitor may not charge before the charger turns itself off or a number of other possible problems, but if might be worth a try.  If you're using a polarized capacitor, + side toward the switch module, - side toward the Pi.
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Sep 16, 2021 13:10
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Cory Parsnipson posted:The intended behavior is that the charger should stay on, delivering current into the battery until full charge and then trickle charge after that. Unless you meant "periodic topping charge," this is not something you should do with 18650s
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Sep 16, 2021 14:14
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Hey dudes. Good or bad commercial project idea - "Smart" home thermostat with a good UI, but cheaper than Nest etc and without the creepy IOT stuff.
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Sep 16, 2021 17:23
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Dominoes posted:Hey dudes. Good or bad commercial project idea - "Smart" home thermostat with a good UI, but cheaper than Nest etc and without the creepy IOT stuff. Isn't that just most other thermostats these days? I mean I guess you could improve the UI a bunch but without internet connectivity you just have a... programmable thermostat, which I can buy from Honeywell for like $30. e: You'd also definitely have to do proper UL testing and FCC approval for anything like that which is designed to be permanently installed in a house so it'd be quite a bit more involved to bring to market than the hydroponics thingy you were making before (that was you right?)
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Sep 16, 2021 18:04
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Dominoes posted:Hey dudes. Good or bad commercial project idea - "Smart" home thermostat with a good UI, but cheaper than Nest etc and without the creepy IOT stuff. On a level playing field it's a pretty good idea, but it's gonna be really really hard to compete with Google's budget, especially with them being earlier to market. You're gonna be up against big brands being pushed by power company incentives. Even without that, most people don't give a poo poo about efficiency as long as it's cold when they get home. Sorry to be pessimistic, I pretty much arrive at this conclusion for things that I personally would love to buy as products too 
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Sep 16, 2021 18:04
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Dominoes posted:Hey dudes. Good or bad commercial project idea - "Smart" home thermostat with a good UI, but cheaper than Nest etc and without the creepy IOT stuff. There are a few open source smart thermostat projects, e.g. HestiaPi. Looks like they're mostly raspberry pi based. I'm not saying they obviate your project, but I think they're more likely to be your competition than the likes of Nest, for what that's worth.
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Sep 16, 2021 18:18
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Thanks for the info! I hadn't considered the regulatory piece. I may just be unlucky, but I've never used a non-Nest thermostat that didn't have a disaster UI for programming. If mine gets in a schedule mode I'm pretty much screwed lol. No idea how to get it to not mess with the temp at random times! I launched the Water Monitor last week, but then put it on pause since I'm out of town for a few weeks. Have 6 built and can build them pretty fast. Need better pics, then will post on HN and some targeted subreddits. Need more pics too eg of it in action. Currently not showing up on any relevant search terms, but hope to change that. I have a few other higher pri projects, so wouldn't start on this for a while, but would like to come back to it after doing some homework on regs, Nest, existing Honeywell etc ones (maybe I've just been unlucky so far with lovely UI thermostats, and many/most are better?), And the RPi stuff. Dominoes fucked around with this message at 18:23 on Sep 16, 2021 |
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Sep 16, 2021 18:20
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Ecobee makes a pretty good one. I had it in my last house. The biggest challenge I would anticipate would be the "cheaper" part. Even leaving aside scale, the creepiness subsidizes the cost for the manufacturer. They monetize the data and pass along the savings, theoretically.
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Sep 16, 2021 19:19
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Looking into Ecobee too. Of note, mine is a Honeywell, and I want to throw it off the balcony. I don't have a good feel for cost. Small temp sensor, color display, (OLED seems apt for a mostly-blank display) basic MCU, and all sorts of parts for mounting interface, enclosure, and mechanical controls. Maybe RF capability in the MCU.
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Sep 16, 2021 19:27
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I don't really get the point of a "smart" thermostat without the IOT stuff. What else do the Nest ones do? The part where it "learns your habits" is bullshit imo and not significantly different from thinking about your schedule for a little bit and programming it appropriately. It's not like your heating/cooling schedule is constantly changing and you're having to always go in and mess with it. It's usually one and done. And while I agree that I don't want my thermostat connected to the internet, I think that's the only other selling point -- preheat the vacation home or whatever. Without that you're just back to the regular programmable one as noted. A better UI would absolutely be great but I think the market for that is infinitesimal (only nerds like us who want a good UI and specifically don't want it to connect to a phone). idk
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Sep 16, 2021 20:58
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I want to be able to schedule things with a sane UI, show both current and target temp etc.
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Sep 16, 2021 21:21
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Stack Machine posted:Oh, I see. That makes it more difficult since then you're bypassing the switch if you just connect it to J8. You could leave the charger on J2 and try a 220μF capacitor between GPIO 6 on the Pi and sense/ctrl on the switch board. This will charge up within a few seconds and turn the PMOS back on if the charger is charging. I won't guarantee it'll work since the capacitor may not charge before the charger turns itself off or a number of other possible problems, but if might be worth a try. That's a cool idea. I tried it this morning and it does keep the charger on, but it also prevents the switch from turning off via the GPIO pin under normal circumstances... I tried putting a lot of capacitance in there instead (3mF) because I figured if it stays below 1ish volts for about 7 seconds, that should be long enough for the switch to turn off. Maybe if I added some resistors, I could increase the charge time. At this point, I think it might be easier for me to just move the switch back to being after the charger and deal with the higher quiescent current. It's just bothering me because it sounds like this switch was designed to do A, B, and C, and it doesn't really do any of them. What am I doing wrong, SparkFun? Tell me your secrets????  KnifeWrench posted:Unless you meant "periodic topping charge," this is not something you should do with 18650s My bad. I meant whatever the charger does when it detects the battery is full. The babysitter handles all of that out of the box.
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Sep 16, 2021 21:39
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Speaking of regulatory nightmares, one of the things I'd really love to make is a niche product for broadcasting analog TV signals within a home. There are things like the Videosender WV-050 on eBay that they seem to have made in the past. That thing takes a composite signal and broadcasts it ~100ft on UHF Channel 15. As far as I can tell, FCC Part 15 only applies to AM or FM radio broadcast frequencies? Or are they actually just talking about the modulation type when they say that? Did the rules used to be different? Were they just sold by companies operating out of foreign jurisdictions at low enough volumes that they just hoped they wouldn't be noticed/prosecuted? I think this is a thing that could find a small niche market in the retro gaming community, lots of people use analog CRTs anyway for the nostalgia & zero-latency aspect. Broadcasted analog video would also be zero-latency and you could have another radio receiver on a PC to capture the stream without more wires too if you wanted. It seems like any product that does anything remotely radio adjacent you have to pay to be tested at a lab and FCC certified, and that $10-15k lab visit per try basically kills this as a product I think. Maybe it could be skirted around for the low volume by being sold as a "kit" that needs some kind of assembly? Assuming you make drat sure it really doesn't spew spurious signals or reach out past 100ft to avoid actually being noticed and pissing somebody off.
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Sep 16, 2021 21:42
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Dominoes posted:I want to be able to schedule things with a sane UI, show both current and target temp etc. I think that's a nice idea and I would probably buy one, but as noted I think almost everyone else will go "duhhhhh but this one doesn't even connect to the internet?? why" 
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Sep 16, 2021 22:37
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LTspice question! I want to simulate a variable source impedance by scanning across the complex impedance plane (i.e., smith chart), then run a noise analysis at each test point. I know the step directive is a thing, but I'm not sure how to handle this case where there are 2 parameters to change, AND, how to deal with the capacitive and inductive halves -- can I specify a reactance explicitly instead of a component value? Alternatively, I'm vaguely aware that LTspice can pull values from external files - maybe I can generate such a file that iterates through my desired range of values?
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Sep 17, 2021 17:00
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Cyril Sneer posted:LTspice question! If you have multiple .step commands they will be nested, or if you want to do some parametric curve around the impedance plane you can step one parameter and then compute the R/L/C values based on that. If you want to switch from a capacitance to an inductance when the impedance goes negative, you can use the ?: operator in the inductance expression to make the C 0 when the impedance goes positive and the L very large when it goes negative. Remember that this is only valid in the neighborhood of one frequency value, since impedance is a complex-valued function of frequency, so it might be fine if this is a narrow-band RF thing, but if you want to do broad-band noise simulations you'll need some representation of the input network, not just the value of impedance at one frequency.
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Sep 17, 2021 18:21
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Got my charge-sensitive preamp working, and it only took the accidental destruction of two of the $12 chips to get there  While it can handle the transient from the power supply coming on just fine, turns out it can't handle the transient of me messing around and connecting probes to the high voltage side. ...or the second time, connecting myself to the high voltage side unexpectedly. That was fun.
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Sep 17, 2021 18:43
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Stack Machine posted:If you have multiple .step commands they will be nested, or if you want to do some parametric curve around the impedance plane you can step one parameter and then compute the R/L/C values based on that. If you want to switch from a capacitance to an inductance when the impedance goes negative, you can use the ?: operator in the inductance expression to make the C 0 when the impedance goes positive and the L very large when it goes negative. I've tried to use multiple .step commands in the past and could never get it to work... Stack Machine posted:Remember that this is only valid in the neighborhood of one frequency value, since impedance is a complex-valued function of frequency, so it might be fine if this is a narrow-band RF thing, but if you want to do broad-band noise simulations you'll need some representation of the input network, not just the value of impedance at one frequency. I only need it at single frequency value.
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Sep 17, 2021 18:58
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Cyril Sneer posted:Alternatively, I'm vaguely aware that LTspice can pull values from external files - maybe I can generate such a file that iterates through my desired range of values?
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Sep 17, 2021 19:12
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Cyril Sneer posted:I've tried to use multiple .step commands in the past and could never get it to work... If you're entering them in the schematic editor I think they have to be in the same text area.
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Sep 17, 2021 19:45
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Shame Boy posted:Got my charge-sensitive preamp working, and it only took the accidental destruction of two of the $12 chips to get there How are the pulses? Do you have some form of multichannel analyzer and a spectrum from one to share? Do you have a schematic of your preamp? I am unreasonably excited about you getting it working and I'm glad you're not dead
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Sep 17, 2021 20:08
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BattleMaster posted:How are the pulses? Significantly better than I expected, to the point where they're clipping pretty bad and I need to swap out some components to crank the gain down. Initially I had simulated this in LTSpice using some incredibly rough calculations of how much energy an alpha particle could theoretically dump into the detector if 100% of its energy was converted to charge. Then I realized that was... probably wrong, so I went and found some academic papers that used 1pC as a test charge to design everything else around, so I went with that instead. Turns out it's a lot closer to the first one I guess, but that shouldn't be too hard to fix. The uncertainty of what exactly the preamp would be spitting out and how much tuning it would need is what drove me to build it first, so I could base the pulse shaper and other downstream bits on actual data instead of guessing. I have a design for the pulse shaper ready to go, just need to adjust some values in it now. BattleMaster posted:Do you have some form of multichannel analyzer and a spectrum from one to share? Nope, that would be why I was asking questions about ADC's earlier, that's the next big thing to design. BattleMaster posted:Do you have a schematic of your preamp? Sure, I'll post it in a sec. BattleMaster posted:I am unreasonably excited about you getting it working and I'm glad you're not dead Thanks, me too  The high voltage was through about 30 megohms so it probably wouldn't have killed me even if it went across my heart or something, but it still left my finger tingling pretty bad for the next few hours.
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Sep 17, 2021 21:14
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Dominoes posted:Hey dudes. Good or bad commercial project idea - "Smart" home thermostat with a good UI, but cheaper than Nest etc and without the creepy IOT stuff. I think you'd have trouble even getting potential customers to know about you since people buying a thermostat seems much less likely to go research stuff than the people that'd be buying your soil sensor.
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Sep 17, 2021 21:37
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I'd be okay buying a sensor ecosystem if it saved me a bunch of time professionally. I probably wouldn't buy something that is only one software bug from burning my place down from an unknown company.
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Sep 17, 2021 21:41
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Went through the KiCad schematic and annotated it so it makes more sense what I'm trying to do. Exported it at a high enough resolution that it looked good on my high-DPI monitor, so sorry for the huge-rear end file if you've got a 1080p one  The input stage is more or less taken from your design, though I lowered the feedback capacitor size due to designing against that 1pC test charge I mentioned. To tone down the output I'm just going to replace that I think. After that is a high-pass filter bit that I referred to as the "derivator" at first, since its output is kinda sorta derivative-like, in that it only cares about the speed of the change in value. However after reading some engineering student's masters thesis and a professor's paper on a similar design I learned that it was (with slight component differences) actually doing pole/zero compensation, so I call it that now. I have to admit, P/Z compensation falls squarely in the realm of "oh god what am I even doing, this is why people go to college for this poo poo isn't it" but I think I sussed out the basic idea thanks to some equations in the papers I mentioned. Basically you want the time constant of C9 and R10/11 to be equivalent to the time constant created by R1/C4, though the actual values can be adjusted to change the gain as long as the time constants are the same. The first half of the TL972 then starts to stretch out the pulse a bit and make it friendlier, and sets its own time constant for the rest of the amplification chain. I'd like to think this is at least one step above cargo-cult engineering but I'm definitely doing something here I don't fully grasp and only really came to understand the behavior of through fiddling with values in the simulator. After that is an output buffer that can adjust for the voltage offset in the TL972's, and add/remove some gain if I need to do that. The actual offset voltage on the output is much higher than it can actually compensate out though (around 100mV) so I need to figure out why that is... Anywhere you see two resistors in parallel it's so I can fine-tune values if I need to. The two DC blocking capacitors on the input are just because I could get 330pF high voltage NP0 capacitors a hell of a lot cheaper than the higher values. Asterisks mean "pay attention to this value", generally cuz it needs to be precise or low tempco. The pulses coming out of it are already reasonably good-looking, so I might not even need the pulse shaper. The design I'm playing with in LTSpice is a two-stage integrator thing that produces very nice gaussian-looking curves with heights highly linearly proportional to the input and pulse widths of about 20us. There's also a trigger circuit that triggers on the preamp output directly so I can gate the measurements. As for the multichannel analyzer, I'm looking at reasonably high-speed ADC's (a few MHz) with 12-14 bits. I figure that gives me enough margin above the 20uS pulse width to average some samples together if I need to, then run sin(x)/x interpolation to get the original waveform back since it's a nice curve and should behave correctly, then find the peak. Current idea is to just connect the ADC to a raspberry pi or something like that and let software do all the heavy lifting with regards to the math, though this is also a perfect excuse to finally learn how to play with that FPGA dev board I got a while ago... Shame Boy fucked around with this message at 22:04 on Sep 17, 2021 |
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Sep 17, 2021 22:01
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Foxfire_ posted:I would do some economics (=wild rear end guessing) for how much profit/unit you think you could make, how many you think you could sell, and what your time is worth. My suspicion is that low volume (relative to something like Honeywell) will make profit/unit low, and that there isn't realistically much of a market for not-expensive, but also not as-cheap-as-possible thermostats, especially when you have to discover that they exist somehow and order them instead of just buying something at the local home depot
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Sep 17, 2021 22:03
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Hello, electronics thread! First time lurker, and first time poster. Electronics was a little hobby of mine when I was younger. The Science Fair 200-In-One Electronic Projects Lab was my introduction, way back in the 80s. That kit was tossed decades ago, but several years back, I bought a new version. I play with it sometimes, and I've made an old fashioned crystal set using directions given out by the government back in the 20s (although I used a diode instead of a cat's whisker). Some day, I'll grab a schematic for a solid state amp (transistor-based A/B), find out what transformers I need, and see if I can make my own little guitar/bass amp the hard way. This is a cross-post from TFR, and someone suggested y'all might enjoy it. I saw this shirt in a YouTube video, and I had to have it. Feast your eyes on your friendly, neighborhood Nothingface--Tarlibone!  ... no, the schematic isn't totally accurate. This is close to an N-channel in enhancement mode, but it isn't quite correct. Still, though, I know exactly one person who gets this joke besides me. So I texted him a picture of me in this shirt with a quick question: Is this a good shirt, or the best shirt? His response? My Buddy posted:That shirt is solid Classic Buddy.
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Sep 18, 2021 00:20
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^^ Welcome! I don't get the shirt. Gotta hand in my EE badge...  Stack Machine, I forgot to thank you earlier for the suggestions. I opened a topic in the SparkFun forums to get some help from one of their service people and now I'm waiting for them to respond. I don't really have high hopes, so I'm gonna put the switch back in its original spot and see if I can disconnect/reconnect the battery when the device is off some other way. Also, Forseti (I think?) posted about the Falstad circuit simulator a little while back and I just remembered about it so I went to check it out. This tool is really well made and has an extremely nice drawing UI! It's perfect for my non-SPICE-havin'-rear end. Turns out it's powerful enough to simulate the power switch schematic and I was able to see it turn on and off:  From off position, closing the (left) switch delivers power to the RPI. The LED turns on.  The RPI GPIO (right) switch going low causes the switch to turn off. This takes approx 5 seconds because instead of a 22uF cap I put in a 10uF cap so I wouldn't have to wait so long. The turn happens around when Vgs of the simulated NMOS drops below 1.5 ish volts.  Pressing down the hardware switch (left) also causes the switch to turn off. The sim time step is so small that this takes forever in wall clock time.  The switch acts as I observe in real life when charging is attached and I try and press down the hardware switch. With the charging happening, the gate of the NMOS on the bottom takes an inconvenient amount of time to turn off. Also the charging voltage source supplies power to the node that connects the two MOSFETs together and that appears to be keeping the top PMOS on. So maybe this is why the RPi turns on when I plug in the power and why if I shut it down and then try and turn it on again, nothing happens (the RPi is expecting an edge somewhere I think). It just looks to me that this circuit wasn't designed to operate with power coming in from the place that the load is supposed to be. The Sparkfun marketing department must have had a hand in writing the feature description because I'm becoming more and more convinced that you just can't use the switch this way.  I guess modern electronics use a more elaborate solution than this.
Cory Parsnipson fucked around with this message at 03:18 on Sep 18, 2021 |
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Sep 18, 2021 03:10
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Cory Parsnipson posted:^^ Welcome! I don't get the shirt. Gotta hand in my EE badge... It's a parody of the classic Misfits wordmark and skull logo T-shirt design. So, getting it means you have to know about MOSFETs and about punk rock bands.
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Sep 18, 2021 03:27
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Oh well either way I'm not cool enough 
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Sep 18, 2021 05:01
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Hey bros. The AirBnb hotub was struck by lightening, and we're trying to make it happen. Any wisdom? 99% change we're hosed, but I'm down for some HTTM if there's a chance.
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Sep 18, 2021 05:06
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