|
poeticoddity posted:Does it have audible continuity testing (I couldn't find that in the listing)? That is the one feature I think is most underrated on low-dollar meters. It's got the symbol for it on the dial but yeah I can't see it in the description...
|
#
?
Nov 15, 2015 22:02
|
|
|
|
| # ? May 8, 2024 20:22 |
|
|
BattleMaster posted:Yeah I would rate that as a must-have feature no matter what. If you want to save money you can deal with, say, autoranging or capacitance/inductance/frequency measurement but audible continuity testing is easily the one feature you never want to do without because of how useful it is for troubleshooting. Agreed. I highly recommend this which is auto-ranging, has audible continuity, current, auto-shutoff for $10 shipped. Because its covered and stores the leads it's also perfect for keeping in a tool bag. The leads are a bit short though and permanently attached. http://www.dx.com/p/auto-range-digital-multimeter-9636#.VkkUla6rRsM asdf32 fucked around with this message at 00:32 on Nov 16, 2015 |
|
#
?
Nov 16, 2015 00:29
|
|
|
asdf32 posted:Agreed. I highly recommend this which is auto-ranging, has audible continuity, current, auto-shutoff for $10 shipped. Because its covered and stores the leads it's also perfect for keeping in a tool bag. The leads are a bit short though and permanently attached. I like how DealExtreme shows it as having a "5.0" rating when like 45% of people rated it a 4 or lower.
|
|
#
?
Nov 16, 2015 00:42
|
|
|
I'm frankensteining together a diy magnetic stirrer and a (proper, lab supply store bought) hot plate. The assembly is fine, but I'm having trouble with the potentiometer regulating the motor's velocity. The setup is a 12v computer fan with a magnet stuck to it, a 10k linear pot and a variable dc source. When I set everything up with the pot putting out the full voltage, the fan runs fine. When I adjust the pot down, everything goes well for about a 1/10th of a turn, and then the fan just stops instead of lowering the rotation speed. It happens roughly at the same place at all voltages up to 12v, and when I run it at 12v there's a slight but definite burning smell coming from the pot. If I skip the pot and just regulate the voltage on the supply it spins fine with as little as 3v. So my questions are: - How hosed is this specific pot? Is it a goner from just the tests or can I use it once I figure out what is it I'm doing wrong? - Would a 1k potentiometer be more useful for this, or would it just burn out as well? - Am I doing it all wrong and should just go die in a fire to save everyone the time? Or, barring that, try my hand at one of the LM317 voltage regulator schematics available online?
|
|
#
?
Nov 16, 2015 18:15
|
|
|
Parallel Paraplegic posted:It's got the symbol for it on the dial but yeah I can't see it in the description... Click on the picture and look at the last one.
|
|
#
?
Nov 16, 2015 18:49
|
|
|
Bubblyblubber posted:The setup is a 12v computer fan with a magnet stuck to it, a 10k linear pot and a variable dc source. When I set everything up with the pot putting out the full voltage, the fan runs fine. When I adjust the pot down, everything goes well for about a 1/10th of a turn, and then the fan just stops instead of lowering the rotation speed. It happens roughly at the same place at all voltages up to 12v, and when I run it at 12v there's a slight but definite burning smell coming from the pot. If I skip the pot and just regulate the voltage on the supply it spins fine with as little as 3v.
|
|
#
?
Nov 16, 2015 18:52
|
|
|
Bubblyblubber posted:I'm frankensteining together a diy magnetic stirrer and a (proper, lab supply store bought) hot plate. The assembly is fine, but I'm having trouble with the potentiometer regulating the motor's velocity. Wait, you're using a 10k pot to control a fan? That won't work because it has 10kOhm of resistance. With the potentiometer fully at one end, there is almost no resistance into the fan, and it works. At 1/10 of the range, the resistance into the fan is 1kOhms, and you can't provide enough current so the fan stalls. Using a potentiometer only works if you know the power consumption of the fan so that you can choose the right size of power potentiometer. EDIT: Measure the current draw at 12V, and then again at 3V. It might not be quite linear, but it will be good enough to let you choose the right value of potentiometer to get a useful range of speeds. Captain Cool posted:The full answer depends on how you have that pot hooked up. In general, though, fans need PWM voltage control. You can build your own or buy one. This works on fans that are meant for PWM control, but not on 2 or 3 wire fans without PWM controllers. Those will just stall if you try to PWM their power pin below a certain duty cycle (if it's a brushless motor). EDIT: Also, make sure that you balance the fan with a second magnet opposite the first. It will still probably fail prematurely due to the axial loading, though, but hopefully not as fast. Slanderer fucked around with this message at 20:54 on Nov 16, 2015 |
|
#
?
Nov 16, 2015 20:48
|
|
|
So there's 3 kinds of computer fans. There's 2, 3 and 4 wire fans. 2 Wire fans are just power and ground. To speed control these with PWM, you'll need to pwm the power going into it. The third wire on a 3 wire fan is an RPM sensor. To speed control these with PWM, you'll need to pwm the power going into it. Unfortunately when you pwm the power the simple way, the RPM sensor starts giving bad data. Basically the power off period can overlap with the RPM sensor's output. A four wire fan is power, ground, rpm sensor, and a PWM input. Here to speed control these you leave power on all the time, and can give a low current signal to the PWM input. Because it's powered all the time, the RPM sensor always works. If you don't care about the RPM signal you can pwm the power anyway, and ignore the pwm pin. The separated nature of the design typically allows for higher speed ranges, which is nice too. I would recommend building a pwm controller, they are more efficient, they don't get hot like a LM317 would, and they can easily control much bigger fans. I've had good experience with them in the past with the speed range. A simple 555 motor driver or buy one. Captain Cool's links are for 4 wire fans, which would probably be better, if you have them.
|
|
#
?
Nov 16, 2015 21:15
|
|
|
For this situation, a PWM controller is completely unnecessary---a power potentiometer is super-simple, really cheap, and the power rating needed here is still tiny for a small fan. It would be improved by adding a polyfuse in series with the pot to ensure that the maximum current is limited (since I'm assuming Bubblyblubber is going to be using a standard 12V wall supply without good overcurrent protection). However, PWM would be superior to an LM317 for this application, since he'll probably be above the safe operating range for using it without a heatsink. EDIT: Whoops, you would actually want a potentiometer + a second small resistor (to limit the current through the potentiometer to ground), I guess. Slanderer fucked around with this message at 23:43 on Nov 16, 2015 |
|
#
?
Nov 16, 2015 23:37
|
|
|
Slanderer posted:For this situation, a PWM controller is completely unnecessary---a power potentiometer is super-simple, really cheap, and the power rating needed here is still tiny for a small fan. It would be improved by adding a polyfuse in series with the pot to ensure that the maximum current is limited (since I'm assuming Bubblyblubber is going to be using a standard 12V wall supply without good overcurrent protection). However, PWM would be superior to an LM317 for this application, since he'll probably be above the safe operating range for using it without a heatsink. There is no need to wire it as a potentiometer as what's really needed is a variable resistor in series with the fan. You can use a pot this way (just use two terminals) or get a two terminal reostat. But wiring that 3rd leg to ground just wastes power with little if any improvement in linearity. Note that if a TO-220 regulator can't handle the heat dissipation the pot is going to have to be pretty large to handle it itself.
|
|
#
?
Nov 17, 2015 01:44
|
|
|
asdf32 posted:There is no need to wire it as a potentiometer as what's really needed is a variable resistor in series with the fan. You can use a pot this way (just use two terminals) or get a two terminal reostat. But wiring that 3rd leg to ground just wastes power with little if any improvement in linearity. You may be right about using the pot as just a rheostat. However, regarding the second point---that is completely wrong. An LM317 w/o a heatsink can handle ~250mW according to google. A 5W 100 Ohm wirewound pot is only like $5 from digikey (that was just the first thing that came up, so you could go cheaper).
|
|
#
?
Nov 17, 2015 02:25
|
|
|
Slanderer posted:You may be right about using the pot as just a rheostat. However, regarding the second point---that is completely wrong. An LM317 w/o a heatsink can handle ~250mW according to google. A 5W 100 Ohm wirewound pot is only like $5 from digikey (that was just the first thing that came up, so you could go cheaper). More specifically, as large as a TO-220, so not a tiny surface mount one (size is the most important thing with heat). A decent TO-220 should be around 50 C/W so 1W or so depending on how much you want to push it.
|
|
#
?
Nov 17, 2015 03:43
|
|
|
asdf32 posted:More specifically, as large as a TO-220, so not a tiny surface mount one (size is the most important thing with heat). It looks like my source might be bullshit (but, actually, I didn't read it very closely). This guy had the goal of limiting the temperature to ~60C, which is not actually unreasonable based on the curves in the datasheet (past 60C the regulator performs worse). Another confounding factor is the thermal resistance (junction to ambient). The first hit on google is from TI, which gives ~20 deg C/W (they had 2 datasheets with slightly different numbers) for TO-220). However, ON and ST's versions of the parts give the thermal resistance as 50-60 C/W, which is a huge difference. Using that resistance, the suggestion of a max of 0.25W makes sense to keep it below 60C if you don't assume ambient is like 25C, but is instead 40C + (which is totally possible inside a poorly-ventilated metal enclosure). Ok, I guess that guy's suggestions are completely reasonable but conservative, which is good from an engineering perspective but not from a hobbyist perspective lol
|
|
#
?
Nov 17, 2015 04:28
|
|
|
asdf32 posted:More specifically, as large as a TO-220, so not a tiny surface mount one (size is the most important thing with heat). From memory I think I think it's around 30C/W for a 3-pin TO-220 to air. Going more conservative is probably better though
|
|
#
?
Nov 17, 2015 10:09
|
|
|
 Following up from the last page, I've put together this rough up for a SPST on switch with a momentary output. My goal is to have the Reset Pin go to the Ground Pin when the switch is first closed. Am I correct that for this to work as I've drawn it I am going to have to jumper the input pin and the ground pin together so that the transistor actually "closes"?
|
|
#
?
Nov 17, 2015 19:05
|
|
|
the wizards beard posted:From memory I think I think it's around 30C/W for a 3-pin TO-220 to air. Going more conservative is probably better though I don't think so. Double checking the highest wattage TO-220 mosfets on digikey turns up a bunch of 60C's That wattage rating is purely theoretical but it's an indicator of how thermally optimized the part is (because it's based on the assumption of a perfect heatsink at the absolute maximum junction). If values much lower than that are printed I'd check the fine print. They may be assuming the TO-220 is soldered to the board and benefitting from PCB sinking, or may be referring to an alternate package. In the case of this datasheet I honestly think it's a mistake or I'm misreading it: http://www.ti.com/lit/ds/symlink/lm317.pdf
|
|
#
?
Nov 18, 2015 01:06
|
|
|
The similiar LM317-N gives it at 23C/W for TO-220. http://www.ti.com/lit/ds/symlink/lm117.pdf
|
|
#
?
Nov 18, 2015 01:10
|
|
|
VanguardFelix posted:
How much time do you want that reset pin driven? Much simpler would be to couple a C (through an R) between S1 out (or the S1 enable signal) and the transistor base. When S1 out goes from ground to 3.3V the C will charge through the transistor base, turning it on until the C is charged to 3.3V.
|
|
#
?
Nov 18, 2015 01:14
|
|
|
Slanderer posted:The similiar LM317-N gives it at 23C/W for TO-220. And it doesn't add up. Note that they cite a junction-to-board for the TO-220 that's less than one quarter the TO-263 (a D2PAK which is a surface mount 220). The TO-220 arguably shouldn't have a junction-to-board and shouldn't beat the 263 by a factor of 2-4 on every metric.
|
|
#
?
Nov 18, 2015 01:29
|
|
|
I would like to build one of these since I'm not in the USA: https://www.adafruit.com/products/1350 http://www.instructables.com/id/EL-Wire-Bracelet/ Does anyone have a schematic?
|
|
#
?
Nov 18, 2015 07:36
|
|
|
Google "EL Wire Inverter Schematic" if you're keen on doing that. If you want a project, that's cool and you should totally do that, just be aware that eBay or AliExpress will sell identical models as Adafruit, usually for less, and free shipping, just about anywhere in the world.
|
|
#
?
Nov 18, 2015 08:03
|
|
|
ante posted:Google "EL Wire Inverter Schematic" if you're keen on doing that. If you want a project, that's cool and you should totally do that, just be aware that eBay or AliExpress will sell identical models as Adafruit, usually for less, and free shipping, just about anywhere in the world. Yeah, I live in Taiwan and would need to use Taobao and I'm not keen on messing with shipping from the mainland to Taiwan yet. I just ordered an ESP8266 and a couple arduinos using ruten. The local shops only have AA powered inverters, I can pull mine apart and look at the transformer. I can head to the electronics emporiums downtown and get all the parts I need in a jiffy.
|
|
#
?
Nov 18, 2015 08:25
|
|
|
asdf32 posted:How much time do you want that reset pin driven? I had toyed with that idea way at the beginning, however I'm just awful at circuits and wasn't sure if that would work. So I overcomplicated things it seems. It looks like I can just simplify the whole thing to the following?  The reset doesn't need to be made long, tenths of a second at a minimum but exceeding that time by orders of magnitude isn't a big deal. If I had a 500 Ohm resistor and a 100 microfarad capacitor I think the charge time would be pretty close. The base amps would be pretty large for the switching I need, but I don't think that will be an issue since we're just trying to short the pins anyways.
|
|
#
?
Nov 18, 2015 13:50
|
|
|
asdf32 posted:And it doesn't add up. Note that they cite a junction-to-board for the TO-220 that's less than one quarter the TO-263 (a D2PAK which is a surface mount 220). I think those numbers are for a TO-220 that's standing and has a heatsink attached. That would explain the low junction-to-board spec too since the main thermal path would be via the heat sink, but there would still be some heating of the board.
|
|
#
?
Nov 18, 2015 16:10
|
|
|
What's a good technique for doing water level sensing? For some dumb reason our washing machine's internal pump can't pump water more than a meter uphill so we've got it pumping into a basin and use a bilge pump to move the waste water into the garden. The system worked well enough, but manually switching on the pump got annoying so I designed a small controller that dangles a pair of wires into the tank and turns on the pump on when the resistance between the wires drops enough. The problem with this is that the wires in the tank tend to accumulate gunk and corrode which increases the resistance and prevents the switch from operating. It's easy enough to fix by cleaning the ends of the wires occasionally, but I'd rather replace it with something that takes care of itself. Any ideas?
|
|
#
?
Nov 18, 2015 17:13
|
|
|
Is power a concern? You can use capacitive sensing to detect water through plastic. It's an active process and consumes power though. The MPR121 is an entry level IC to do it. The other alternative that you see on things like a Keurig is a magnet on a floater with a Hall effect inside.
|
|
#
?
Nov 18, 2015 17:33
|
|
|
travelling wave posted:What's a good technique for doing water level sensing? I’m a fan of using an ultrasonic sensor to measure the distance to the surface of the liquid. It requires no contact with the liquid and therefore cannot be fouled. Measuring the weight of the container is another no‐contact option, e.g. via a load cell on one corner. e: Pressure sensors with large diaphragms are pretty robust as well. Platystemon fucked around with this message at 17:44 on Nov 18, 2015 |
|
#
?
Nov 18, 2015 17:40
|
|
|
At work we use ultrasonic level sensors to get an analog signal but I think you can use a float switch.
|
|
#
?
Nov 18, 2015 17:42
|
|
|
bred posted:At work we use ultrasonic level sensors to get an analog signal but I think you can use a float switch. Float switches are probably the best bet. They are reliable and don't need complex calibration. This application doesn't actually need to sense the water level, just turn on the pump if there is enough water present. EDIT: Also, part of his problem is using wires as electrodes, and probably using DC sensing. To do impedance-based fluid detection, you want to use plated electrodes (idk, probably gold or silver plated?), mounted a fixed distance apart before a small filtering element (to prevent large debris from going between the electrodes), and probably use AC sensing to minimize whatever weird electrochemical effects might occur. Slanderer fucked around with this message at 18:10 on Nov 18, 2015 |
|
#
?
Nov 18, 2015 18:07
|
|
|
VanguardFelix posted:I had toyed with that idea way at the beginning, however I'm just awful at circuits and wasn't sure if that would work. So I overcomplicated things it seems. It looks like I can just simplify the whole thing to the following? Yes. As drawn the circuit leaves the possibility of the S1 out net being left floating (if nothing is on the input pin) which could prevent the circuit from discharging and retriggering. Add a pull down there (unless the input is reliably tied to ground). Size the R to provide the base current you need at, say V(S1 out)/2 and then size the cap to give you the time you need. I'd be aiming for a smaller cap than 100uf which is unusually large and probably unnecessary for signal work. A fet would consume zero current itself so it would give you more flexibility in terms of components here (though I like BJTs for their added robustness sometimes).
|
|
#
?
Nov 18, 2015 18:17
|
|
|
travelling wave posted:What's a good technique for doing water level sensing? Float switches are an inexpensive and reliable option as others have said. Look up saltwater and freshwater aquariums systems for replacing evaporation a.k.a. auto top off systems. These guys are my go-to for float switches (and solenoids, fwiw): http://autotopoff.com/products/ Excellent, well-priced products and even better customer service.
|
|
#
?
Nov 18, 2015 19:43
|
|
|
Slanderer posted:Float switches are probably the best bet. They are reliable and don't need complex calibration. This application doesn't actually need to sense the water level, just turn on the pump if there is enough water present. I use float switches in my aquarium's sump for topoff control and they're usually great. The only issue with float switches is the possibility that whatever gunk is accumulating on the existing solution could also gunk up the float switch and cause it to stick, which depending on how it's wired would either end up pumping dry or not pumping at all. If you'd be worried about that then consider using multiple float switches to control failsafes. I have one float switch in my sump to activate a pump which adds freshwater from a reservoir and a second switch in the reservoir that prevents the pump from activating if it's empty. An additional level of safety would be a "high mark" switch in the sump to stop the pump in case the main one gets stuck on but in my case that's not an issue (the controller shuts off the pump after 10 minutes of continuous operation).
|
|
#
?
Nov 18, 2015 19:52
|
|
|
csammis posted:I use float switches in my aquarium's sump for topoff control and they're usually great. The only issue with float switches is the possibility that whatever gunk is accumulating on the existing solution could also gunk up the float switch and cause it to stick, which depending on how it's wired would either end up pumping dry or not pumping at all. This is all great stuff. I like tethered float switches. I got one on a LONG (5m) cord for $10 from grainger back in the day. SPDT: one contact would make when it floated above a certain angle, one contact would make when it dropped below another. I wired a control relay to actuate a sump pump, and it worked a charm. edit: It's still made.
|
|
#
?
Nov 19, 2015 02:09
|
|
|
Thanks guys. I found some float switches on ebay for  so I'll give them a try.JawnV6 posted:Is power a concern? You can use capacitive sensing to detect water through plastic. It's an active process and consumes power though. The MPR121 is an entry level IC to do it. It needs to be wall powered to run the pump, so power isn't an issue. Capacitive sensing is an interesting idea, the holding tank/basin is essentially a large concrete tub so mounting the sensor so it comes close enough to the water would be difficult. A long test tube might work... Slanderer posted:Float switches are probably the best bet. They are reliable and don't need complex calibration. This application doesn't actually need to sense the water level, just turn on the pump if there is enough water present. I do have a bunch of SR04 ultrasonic range finders lying around that I could use. I don't think the calibration would be much beyond waving a sheet of paper in front of it to set the trigger level so I might try that too. Slanderer posted:EDIT: Also, part of his problem is using wires as electrodes, and probably using DC sensing. To do impedance-based fluid detection, you want to use plated electrodes (idk, probably gold or silver plated?), mounted a fixed distance apart before a small filtering element (to prevent large debris from going between the electrodes), and probably use AC sensing to minimize whatever weird electrochemical effects might occur. Yeah it's using DC sensing, here's the whole schematic. Gold/sliver plated electrodes are probably overkill, but I was considering was using some old stainless steel butter knives as electrodes.
|
|
#
?
Nov 19, 2015 04:19
|
|
|
asdf32 posted:I don't think so. Double checking the highest wattage TO-220 mosfets on digikey turns up a bunch of 60C's IIRC it was on an appnote comparing different packages, I think free standing. A quick google doesn't turn it up though so I could be wrong. In these cases I would usually leave a pretty huge safety margin and then get some measurements of the outside of the package once it's built. e: found a local copy and google brought up the original http://cds.linear.com/docs/en/packaging/Linear_Technology_Thermal_Resistance_Table.pdf the wizards beard fucked around with this message at 09:22 on Nov 19, 2015 |
|
#
?
Nov 19, 2015 09:18
|
|
|
travelling wave posted:It needs to be wall powered to run the pump, so power isn't an issue. Capacitive sensing is an interesting idea, the holding tank/basin is essentially a large concrete tub so mounting the sensor so it comes close enough to the water would be difficult. A long test tube might work...
|
|
#
?
Nov 19, 2015 19:49
|
|
|
So thanks to solderchat a few pages back, I ordered a roll of random Chinese 63/37 stuff. However, all of my joints were coming out dull, and after poking around google, it turns out there are huge quality differences between different brands. False economy strikes again.
|
|
#
?
Nov 21, 2015 19:00
|
|
|
Just use lead-free solder. Then ALL you joints will come out dull 
|
|
#
?
Nov 22, 2015 03:41
|
|
|
I got a cheap 24v transformer of sufficient VA rating for my needs but now I have no idea which end is which. What's a safe (read: non destructive) way of determining which end to put mains power into?
|
|
#
?
Nov 25, 2015 08:32
|
|
|
|
| # ? May 8, 2024 20:22 |
|
|
Spookydonut posted:I got a cheap 24v transformer of sufficient VA rating for my needs but now I have no idea which end is which. Without thinking too hard about it, I would try to measure resistance of each coil and compare. Turns ratio should be sorta related to length, which should be related to ohms. it's going to be a small difference though, milliohm ranges most likely, so this may not be great solution.
|
|
#
?
Nov 25, 2015 10:04
|
|
