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I have a laptop LCD screen - http://www.amazon.com/gp/product/B004935KDQ I ordered it to replace a cracked screen in a friend's laptop but it turned out to be the wrong model. Is there any way of interfacing it to something like an ARM or x86 development board, maybe something targetted at laptop developers? I have no idea how standardised laptop graphics interfaces are.
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Aug 17, 2011 17:11
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Hillridge posted:That was me actually. Adding capacitance fixing the problem makes me think it's a hardware issue with the nets connected to CONF_DONE (you probably can't share the schematic). Then again, maybe that pin is being set to something else post-programming as well.
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Aug 18, 2011 04:08
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movax posted:Adding capacitance fixing the problem makes me think it's a hardware issue with the nets connected to CONF_DONE (you probably can't share the schematic). Then again, maybe that pin is being set to something else post-programming as well. It's a pretty simple net, and something I've used before without issue. The conf_done net goes between the micro and the FPGA with a 10k PU to 3.3V. it also goes to the ~OE line on a couple buffer chips to disable them once the FPGA is programmed. I have a 0 ohm on this line, so I'll try disconnecting it and seeing if the issue goes away. I'm also going to double check that this line requires a 3.3V PU and not a 2.5V.
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Aug 18, 2011 16:46
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Hillridge posted:It's a pretty simple net, and something I've used before without issue. The conf_done net goes between the micro and the FPGA with a 10k PU to 3.3V. it also goes to the ~OE line on a couple buffer chips to disable them once the FPGA is programmed. I have a 0 ohm on this line, so I'll try disconnecting it and seeing if the issue goes away. I'm also going to double check that this line requires a 3.3V PU and not a 2.5V. Also try adding 1 to 10 pF to ground on the line, since that's what your probe is anyhow. This isn't a solution, but it'll give you some evidence as to the source of the problem. If it wants a 2.5V pullup instead of a 3.3V pullup you're probably not hurting much by using the latter. The high side parasitic body diodes and/or ESD diodes on the output driver are going to sink some current from the 3.3V supply into the 2.5V supply through the 10k resistor when things are pulled up, but those devices are designed to conduct a hell of a lot more than 20 microamps. (OK, in principle it's possible that the chip's ESD strategy is based on a transient clamp and the output devices are in a floating well that isolates the parasitic diode, but the only time you generally see that is when the inputs are tolerant of a higher voltage than the supply voltage of the chip, which would still imply that you're safe.)
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Aug 18, 2011 23:06
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movax posted:My problem isn't with the Arduino so much, it's more some Arduino users running around after writing a few sketches believing they're embedded experts and dispensing horrible advice (i.e. not every problem in the world calls for an Arduino, nor can it be solved by an Arduino). Nothing's more frustrating than having a guy who used an Arduino once getting pissed at you because you're not listening to his "expert advice" about using an Arduino plus some obnoxiously priced PWM shields to control a DC/DC converter as opposed to a $6 one-chip solution with a dsPIC. You would be a good person to ask. I have an adruino and so far all I've done is play around with it using its own IDE (though I've written C code to communicate with it after the fact). I'd like to start coding in pure C/C++ and do the compiling and downloading myself. Do you know of any good sites that describe the process? I'm quite competent with coding, I just don't know much about what libraries and compiliers I would need to do this.
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Aug 19, 2011 02:21
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And then watching like 12 other people run out and drop $75 on "maker kits" that are essentially an Arduino + LEDs + insane markup.
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kwantam posted:Also try adding 1 to 10 pF to ground on the line, since that's what your probe is anyhow. This isn't a solution, but it'll give you some evidence as to the source of the problem. Oh it's definitely something to do with capacitance. I've already "fixed" the problem with an 18pf cap to ground. A well placed finger also works. I also managed to make it work without a cap (or finger) by removing the ~OE inputs from the net. Basically the conf_done line was connected to an input on my micro and to the ~OE pins on two sn74lvc1g125 buffer chips. Removing the buffers also fixes it. Next step is to try a harder pullup. Edit: 5k pullup makes it worse! Digging up the number for my FPGA rep. Hillridge fucked around with this message at 18:31 on Aug 19, 2011 |
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Aug 19, 2011 16:47
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Cyril Sneer posted:You would be a good person to ask. I have an adruino and so far all I've done is play around with it using its own IDE (though I've written C code to communicate with it after the fact). I'd like to start coding in pure C/C++ and do the compiling and downloading myself. Do you know of any good sites that describe the process? I'm quite competent with coding, I just don't know much about what libraries and compiliers I would need to do this. I don't know that many AVR sites off-hand, but briefly all you would need is: - stand-alone programmer - Atmel IDE (I think AVR Studio is what it's called). This will include the compiles and includes you need to get started. And you're off to the races. It'll create an output hex file you can feed to the programmer, or if the IDE is nice, you can have it auto-download the code to your chip after every compile. General form for a C program is always having #include <modelnumber.h> so you can refer to the ports or what not. So for my PICs, I could do #include <p18f1640ga101.h> or something, and I have all my definitions (PORTA, PORTB, etc etc). Looking for application notes from the manufacturer is always good too. I crib Microchip ANs all the time, they save me hours.
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Aug 19, 2011 18:02
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I got a new toy yesterday. A DSO Nano. I'm pretty pleased with it so far. That said, I'm a noob, and the concept of "graphing voltmeter" still gets my manbits tingly. What I have found so far, is that it can handle up to 60v input, and down to 500mv. It has a 1mhz sample rate, with a 12 bit DAC. It has a built in test signal, that can be varied from 500-2000hz, and 50-99% duty cycle. It has an adjustable trigger, and how ti triggers can be chagned. It has adjustable display offset. Uh.... I"m still exploring.
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Aug 21, 2011 05:11
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Nerobro posted:I got a new toy yesterday. A DSO Nano. I'm pretty pleased with it so far. That said, I'm a noob, and the concept of "graphing voltmeter" still gets my manbits tingly. Yeah, I'd looked at that guy, along with the newer DSO Quad. I've never read a professional review of either, but my concern has always been a that the analog front end might be subpar, because they are frankly really, really complicated when dealing with RF signals. So, I really just don't know how well things are shielded, how well that part of the board is layed out, if they inputs are properly ESD protected. Then there's the element of accuracy and stability (versus temperature, aging, etc) of the readings. Heck, I got this piece of junk when it was brand new, but only because I was an eager youth, and it seemed neat (and cheap). The "gets my manbits tingly" comment seems oddly applicable to how I felt. But it nly took a few minutes for even me to realize that I couldn't really do much of anything with it. Clearly, they've gotten rather better since then, but pocket scopes still seem to have limited utility. Still, though, the biggest issue I have is actually just the tiny LCD screens. I'll go with my old CRT-based displays, thank you!... ...well, until I buy a modern scope, that is. The DS1052E is a few years old by now, but it's still pretty high quality (for the $400 price, that is).
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Aug 21, 2011 06:39
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I bought one of those DIY scopes too. I blew up a couple of the caps building it, so it didn't ever work for me. I still have the kit. Perhaps I can scavenge the AVR and display.
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Aug 21, 2011 08:58
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Ok, this isn't really DIY electronics, but it's still pretty relevant (and I can always ask in SH/SC): So, I've worked on a lot of projects that never left my workshop, and learned a lot of really useful crap in general. I'd definitely like to be able to share this, and probably in the form of a blog. That way, I can document my projects, link to source files on github, and provide a venue to submit my projects to places like Hack a day. Thing is, I haven't made a website since Freshman year of college (wherein we used some fancy, expensive program to make a two-level site, following a tutorial step by step, hosting it on our publicly accessible URL that they provided). So, essentially, I have no idea where to start. Clearly I need to register a domain name and pay to get it hosted somewhere, but besides that, I don't know where to start. I mean, I've heard of things like Wordpress, but I don't know what the gently caress. Also, if I can keep my blog regularly updated with projects, and with a sufficient numbers of viewers, I'd probably want to make the blog just part of a larger site, so I could sell stuff as well (using another premade solution). So, any suggestions? I'm about to start a quick project to make a wifi+clock controller IR remote for the air conditioner in my new apartment (so I can have it turn on a set time before I get home, w/ time depending on out side temp). I'd really like to start from more basic stuff as well---how I determine the frequency and encoding of the IR remote (I know TV remotes are usually 38kHz, but they make demodulator packages in different freqs), perhaps a rough estimate of the wavelength, and all that stuff.
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Aug 21, 2011 18:27
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Do varicap diodes have bad ESR? I'm debating between using them or making an electronically switched capacitor network but i'm not really sure which would have the lower resistance, but i would assume the network.
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Aug 22, 2011 20:05
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I checked a random handful varicap diodes on digikey and saw ESRs in the .3 to 3 Ohm range. What will you use to do the switching? I would think you could find something with lower resistance than 3 Ohms without huge difficulties, but .3 will be harder to beat. The last 16-channel mux I used is nominally 4 Ohms and it was pretty much the lowest resistance I could easily get.
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Aug 22, 2011 20:28
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Wouldn't you attain lower ESR by using more capacitors in parallel? I was thinking of using FET's for switching.
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Aug 22, 2011 21:04
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Pizer posted:Wouldn't you attain lower ESR by using more capacitors in parallel? Good FETs can get you well under 300 mOhms. What are you planning on doing with this switched cap network though?
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Aug 22, 2011 21:13
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SnoPuppy posted:Good FETs can get you well under 300 mOhms. What are you planning on doing with this switched cap network though?
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Aug 22, 2011 21:17
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Pizer posted:Seeing if it's possible to do automatic RF matching What frequency ranges? You're really going to want to use a good GaAs FETs for anything that is above a few tens of MHz. You also shouldn't be as worried about the DC resistance as much as the S parameters of the switch in question.
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Aug 22, 2011 21:44
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SnoPuppy posted:What frequency ranges? I'm pretty new to RF, I'll have to look into that. the switching frequency itself is irrelevent, just needs to pass those frequencies. Thanks
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Aug 22, 2011 22:04
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I don't think your typical switching FET has particularly good RF on characteristics even at VHF frequencies.
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Aug 22, 2011 22:14
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Varicap diodes have always blown my mind since I first read about them, but I haven't been able to get any good education about their practical uses, unfortunately. Although I did find it neat that the Rigol oscilloscope that people hack to increase the bandwidth + sampling rate uses a varicap to change input low pass filter response in software.
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Aug 22, 2011 22:17
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I'm looking to drive a 9V relay from the output of a MSP430G2xx pin that's running at 3 Vcc. Can someone point me to some reading material on how to boost the voltage from the pin? Should I isolate the relay from the microcontroller somehow? Thanks!
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Aug 22, 2011 22:21
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csammis posted:I'm looking to drive a 9V relay from the output of a MSP430G2xx pin that's running at 3 Vcc. Can someone point me to some reading material on how to boost the voltage from the pin? Should I isolate the relay from the microcontroller somehow? Use a transistor to switch the coil of the relay on: http://www.mcuexamples.com/PIC-Relay.php You will need to get 9V somehow. Does your board have a higher voltage rail or do you only have 3V available?
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Aug 22, 2011 22:25
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The dev board is a Launchpad running off a USB line so it's not readily available...what if I had a power source running at 9V, how would I downconvert the voltage so that the uC has a 3V rail to work with?
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Aug 22, 2011 22:29
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Pizer posted:about 50-150MHz For those frequencies you should be able to get some cheap GaAs SP4T or SP8T switches. Those will let you switch your common RF to 1 of four or 1 of eight outputs, which in your case could be caps/inductors. Since you only care about stuff up to 150 MHz, you probably won't have to worry about transmission line effects too much either, so the PCB shouldn't be that bad. edit: Look at Skyworks/RFMD stuff - it's usually pretty cheap and should be fine for your use.
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Aug 22, 2011 22:40
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csammis posted:The dev board is a Launchpad running off a USB line so it's not readily available...what if I had a power source running at 9V, how would I downconvert the voltage so that the uC has a 3V rail to work with? You would use a voltage regulator to go from 9V to 3V. If you are running off USB, you will have 5V. Can you find a 5V relay to use instead of the 9V relay?
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Aug 22, 2011 22:51
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csammis posted:The dev board is a Launchpad running off a USB line so it's not readily available...what if I had a power source running at 9V, how would I downconvert the voltage so that the uC has a 3V rail to work with? You need a regulator either way, one to buck a higher voltage down to 3.3 or 5V to feed yoru board, or a boost to generate 9V. I recommend the former approach, and finding a 12V supply somewhere, if you can't switch to a 5V relay. Or maybe switch to a 12V relay, as they are really really common in that voltage.
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Aug 22, 2011 22:56
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Pizer posted:Seeing if it's possible to do automatic RF matching This can and has been done with varicaps in some applications. However it only really works well when tuning in a small range. Like if you want to adjust a 100pF cap by +5-10pF, a varicap will be fine even if its ESR is high (since it won't increase the losses of the overall cap much). But if you want a 10pF cap with a +5-10pF range, you've got a problem because now that varactor is going to contribute a lot more to losses. If you actually want to tune over a large range (like more than +/-10%) while maintaining very low losses, then you'll be looking at switched components. And solid state switches generally won't cut it; PIN diodes are an option, but RF relays are often the best choice.
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Aug 23, 2011 01:13
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Slanderer posted:So, I've worked on a lot of projects that never left my workshop, and learned a lot of really useful crap in general. I'd definitely like to be able to share this, and probably in the form of a blog. That way, I can document my projects, link to source files on github, and provide a venue to submit my projects to places like Hack a day. Thing is, I haven't made a website since Freshman year of college (wherein we used some fancy, expensive program to make a two-level site, following a tutorial step by step, hosting it on our publicly accessible URL that they provided). So, essentially, I have no idea where to start. Clearly I need to register a domain name and pay to get it hosted somewhere, but besides that, I don't know where to start. I mean, I've heard of things like Wordpress, but I don't know what the gently caress. Also, if I can keep my blog regularly updated with projects, and with a sufficient numbers of viewers, I'd probably want to make the blog just part of a larger site, so I could sell stuff as well (using another premade solution). I don't have any advice but maybe related is what electronics blogs/sites do you read/watch. I usually check out http://hackaday.com/ and http://www.eevblog.com/. So what sites/blogs do people here read? On another note I designed my first PCB. I got it printed and soldered everything to it and it actually worked. That's for all your help in the thread earlier. The main problem I had was I initially soldered in a LF33CV instead of a LD33CV which have different pinouts  It didn't take me long to find out that was the problem since I used the tried and true method of seeing what component burns your hand. Is there any reason that the LDO have different pinouts? I tried my best with the vacuum solder pump thing and solder wick but just couldn't get rid of enough solder so it ended up quite messy. Is it worth buying a cheap heat-gun to de-solder components? Any comments on the design layout or soldering? Links. Edit: I don't know where to host images, image"shack" didn't work. Check post below I want to move into SMD PCBs and was wondering how important is soldermask. Would it be possible to solder SMD stuff as a novice on a naked board without solder mask? Note: I have nothing to do with spirit circuits I just used their free PCB service which means they stuck all that advertising over the PCB. I left it there since I was quite impressed with their 72 hour free PCB prototype service. FSMC fucked around with this message at 00:05 on Aug 28, 2011 |
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Aug 27, 2011 23:44
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Photos for above post.
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Aug 28, 2011 00:04
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Can someone point me towards a resource which can help me with a frustrating hole in my knowledge? I've a pretty well rounded knowledge of things but I am seriously lacking in knowledge on how to deal with some analog interfacing. Most specifically ways to measure / out put the equivalent of variable resistance, and all possibly at higher than logic level voltages. I'm asking because I feel like doing another microcontroller project. I build all my stuff from scratch so no arduinos and that sort of thing. What I was considering doing was a fuel gauge adapter for my VW. Ie. Measuring the sender resistance, applying some correction for the shape of the fuel tank, averaging the value to counter the fuel sloshing around, and outputting a compatible signal for the gauge I have. Yes I know it's pretty pointless but it does allow me to add on more advanced features such as fuel economy calculations etc. I have measuring distance / velocity covered so don't you worry about that. Most of this is easy for me except I'm a bit retarded where it comes to the correct method for sampling a varying resistance. I can probably just say "screw it" and do a PWM output for the gauge. All I want to know is how do I measure resistance for use with a microcontroller?
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Aug 28, 2011 02:05
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General_Failure posted:All I want to know is how do I measure resistance for use with a microcontroller? Create a voltage divider between a known resistance and your sender, then measure the voltage in the divider. Pick a sensible resistor for the known resistance and you should be fine. You didn't provide any numbers so I don't know what a good guess would be, but this example from MIT with a photoresistor is pretty much the same thing. http://web.mit.edu/rec/www/workshop/photoresistors.html Replace photoresistor (resistance changes with light levels) with your fuel gauge (resistance changes with fuel level), and hook it up to your ADC port. Once you've measured the value, you can do whatever work you need to as far as filtering it or adjusting it.
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Aug 28, 2011 02:14
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Delta-Wye posted:Create a voltage divider between a known resistance and your sender, then measure the voltage in the divider. Pick a sensible resistor for the known resistance and you should be fine. You didn't provide any numbers so I don't know what a good guess would be, but this example from MIT with a photoresistor is pretty much the same thing. I'll see what I can dig up for numbers later on. I know the figures exist as I have seen them. they are just a little hard to find. I totally forgot about voltage dividers. For shame. I've had to use them for a custom interface I built a few years back.
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Aug 28, 2011 03:44
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Unparagoned posted:I tried my best with the vacuum solder pump thing and solder wick but just couldn't get rid of enough solder so it ended up quite messy. Is it worth buying a cheap heat-gun to de-solder components? Any comments on the design layout or soldering? The trick to wicking solder is actually applying a glob of fresh solder to the back of the wick. It doesn't make any sense, but if you add tons more solder, the heat transfer is good enough to liquify the solder and make it wick really, really well. I tried it once out of frustration with my wick when I was a lil baby engineer, and I was blown away when I picked the wick up and revealed totally bare contacts.
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Aug 28, 2011 16:45
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It also helps to put lots of flux down. That way, the solder will easily flow into the wick.
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Aug 28, 2011 22:24
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Would anyone like to explain some bits of this circuit to a noob? I'd put together a simple varistor-voltage divider -> PWM chip -> transistor -> 3V toy motor circuit that worked fine. I then payed a fellow to design a more professional version for me and then lost the ability to contact him. I'm curious how to characterize: - what the function of the two op-amps is - why there are three transistors in the path to the motor It looks like the op-amps form a multiplier feeding into a difference amplifier so that the voltage going out the ADC line is ultimately around 0.02 times the Vin, but I'm not sure why you would want to do it that way. Also, I can't really tell where the Vin is coming from. Is it being supplied by some value the microprocessor is programmed to put out via the ADC pin? The three transistors, I have no idea there are three instead of one. 
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Aug 29, 2011 04:26
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Unparagoned posted:Is it worth buying a cheap heat-gun to de-solder components? Any comments on the design layout or soldering? Oh, a flux pen will help when using wick/braid. It really helps to add more flux when using wicking away the solder. You don't necessarily need a flux pen, just drip some flux on. taqueso fucked around with this message at 04:41 on Aug 29, 2011 |
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Aug 29, 2011 04:38
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ReleasetheKracker! posted:Would anyone like to explain some bits of this circuit to a noob? The opamps are used to measure the voltage across the flex sensor. The DAC is used (I'm assuming) to calibrate out the imbalance of the resistors R4/R9 if you want. It also looks like the opamps default to the power down case (the SD_bar pins are pulled low). The 3 transistors are used to enable/disable the motor during calibration. If TP5 is pulled high, Q2 and Q3 will be off. If TP5 is low, Q3 and Q2 will turn on whenever Q1 turns on. I'm pretty sure this is more complicated than it needs to be, but I think it should work. I'm not sure what you mean by "I can't really tell where the Vin is coming from." It looks like the input power comes from a pin header and is "regulated" with a Zener. I will say that if you're actually trying to take precision measurements, the crappy power regulation combined with the motor will make it tough.
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Aug 29, 2011 06:08
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"I can't really tell where the Vin is coming from" means I can't see where a positive voltage is entering that part of the circuit so that it drops across the flex sensor/voltage dividers. Sorry about not being clear. I don't really know what the DAC line is doing. Is it for a voltage exiting the microprocessor? I'm assuming it isn't an analog voltage entering the microprocessor unless I am misunderstanding what DAC means here. Oh, are you saying the power comes via that pin labelled TP2? Thanks for responding. It is really cool to realize you can make something that seemed so arcane and out of reach.
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Aug 29, 2011 07:21
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SnoPuppy posted:The 3 transistors are used to enable/disable the motor during calibration. If TP5 is pulled high, Q2 and Q3 will be off. If TP5 is low, Q3 and Q2 will turn on whenever Q1 turns on. I'm pretty sure this is more complicated than it needs to be, but I think it should work. SnoPuppy posted:I'm not sure what you mean by "I can't really tell where the Vin is coming from." It looks like the input power comes from a pin header and is "regulated" with a Zener. ReleasetheKracker! posted:"I can't really tell where the Vin is coming from" means I can't see where a positive voltage is entering that part of the circuit so that it drops across the flex sensor/voltage dividers. Sorry about not being clear. FYI TP is "test point," so I wouldn't say the "power comes" via that pin, it's mostly debugging and such. For instance, if I wanted to know what the gently caress the PIC was doing with it's DAC pin, I would scope TP2 and see what's up.
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Aug 29, 2011 08:26
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I have to write the PIC code. I'm a software guy and someone else is building the circuit for me; unfortunately, it isn't the guy who designed it, so I am learning circuits now. I think SnoPuppy is right about the transistors being used in calibration. Some of those pins labelled TP# are to be pulled high or low to get the max and min flex values for calibration. He is also correct that the op-amps are set to sleep on boot until a power switch is pressed. So, anyway, I'm trying to build the thing on a breadboard and I didn't see a branch labelled 3V connecting to the flex sensor section of the circuit. It's a pretty fancy microcontroller, because I want it to be able to retain some learned-from-use data. So let's see.. the data sheets says control bits can be set such that the DAC voltage level is set to Vdd and output on the DACOUT pin. Which would be 3V. OK, that sounds right. Sound right to you guys? Cool stuff. Cool, cool, cool. It feels really good to make a mental breakthrough.
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Aug 29, 2011 09:02
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