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1  Using Arduino / General Electronics / Increase voltage drop on: March 01, 2013, 04:41:57 am
Hi guys,
           I am still working on my alternator/generator setup (see magneto interference in motors sect.) and have come against another problem. I have a 100A - 100mA shunt that I'm trying to use as an amp guage. I understand all the logic and have the code working with all the float values correctly.

 I'm reading 15v dc and I have wired both sides (indipendantly) through a 1k resister to arduino input and then a 500 ohms to ground which (theroreticaly) gives me 5v signal. All is good there and multimeter is testing at 4.2v.
The problem is that I read pin A4 and calculate volts, then send it to LCD, then I read A4 and A5, subtract them and calculate to read amps (voltage drop) and send that to LCD. It seems that the resolution of the analog in is not great enough to read the tiny amount of voltage drop as I have tried both float and double and the increments are to large. I don't need it to be exact, just a little more readable than 8A chunks.

This is where I need help. I was wondering if it was posible to cross ref the two signals and somehow amplify the voltage drop in the second signal (A5). I can calibrate it with the code no worries and that should fix the resolution problems. I'm not too sure as how to do it because I'm only new to electronics and only know the basics. I am really sorry I can't post the code or draw a wire diagram for you. I only have mobile Internet because of all the rain and flooding!! Hope it stops soon!
2  Using Arduino / Motors, Mechanics, and Power / Re: Magneto interference with arduino on: February 27, 2013, 12:25:58 am
Chagrin, I saw your post and thought "don't be stupid, everything has one now" but I did check and I guess the Chinese don't use them unless they have to. Swapped it to a Bosch "R" type plug and everything is fine. Peeved me off because I normally do the simple things first, but if it weren't for you, I'd still be off trying other things. I have found that I still need decoupling on the power supply, which is a big help but now with both, no errors at all. A big thanks to both of you for your help!
3  Using Arduino / Motors, Mechanics, and Power / Re: How can I protect my Arduino from current spikes? on: February 25, 2013, 04:37:44 am
Just a point for future reference, you can not protect from voltage spikes by using code. Yes, sometimes well written code can help prevent voltage spikes in some of the outputs, but as a general rule, it has to be protected by electronic components, ie capacitors. Particularly on the power supply as it is out of control of the arduino. Although it is correct that there would be little feedback if there is an external supply. If you wanted to be extra careful, you can put a diode reverse bias across the motor poles, or if the motors run both forward and reverse, two opposing Zener diodes in series with a voltage rating just a bit higher than the motor.
4  Using Arduino / Motors, Mechanics, and Power / Re: Magneto interference with arduino on: February 24, 2013, 11:34:47 pm
No, I haven't tried that, my biggest problem is room as I'm trying to make it as small as possible. This means that everything is close together and I do know that when I diagnose on cars and things, the ht lead can interfere with my multimeter, and it is not a cheap one either. Given that knowledge, and the fact that the whole generator is around a 12 inch cube, I'm led to believe that it is the ht lead that is causing it. As mike said, it is a matter of what is true, and I don't have the correct test equipment yet, I have to go on my gut feeling. I am having a small bit of success with the decoupling capacitors but I haven't had a lot of time to play with it. I will keep you posted.....
5  Using Arduino / Motors, Mechanics, and Power / Re: where to find 4-wire suitable steppers? on: February 24, 2013, 03:42:31 pm
For steppers, try eBay as mike said, there is a fair few of them with all sorts of ratings. Yes it might be a bit more, but it is less headache if they are the correct size you need, and all six are the same. Try looking under CNC stepper......
6  Using Arduino / Motors, Mechanics, and Power / Re: Distance Specified Cutoff on: February 24, 2013, 02:51:05 pm
The easiest solution would probably be a Hall effect type sensor on one axle. For example,
Mount a disk on one axle with slots cut in it and use an optical sensor to count the pulses. The more slots on the disk, the more accurate the distance. The motor would be indipendant if needed and receive the control from arduino. If you mounted the disk on the motor itself, you have basically made a servo motor, and that is what they use to control CNC machines with acruacies down to 0.001mm. Although they are a little more sophisticated, the idea is the same. With a servo type
System, you can set it up to be closed loop as well, this basically means that I'f the motor stalls or jams, the board can "see" it and report an error to you and it will always read the actual position, not where it thinks it is.
7  Using Arduino / Motors, Mechanics, and Power / Re: Magneto interference with arduino on: February 24, 2013, 07:09:23 am
Awesome, thanks again, it is certainly a lot more in depth than I imagined! I'll give it all a go in the next few days and let you know how I get on. This project might be the perfect excuse to buy that scope I've been putting off, he he he.
8  Using Arduino / Motors, Mechanics, and Power / Re: Magneto interference with arduino on: February 24, 2013, 04:01:39 am
Thanks, I will keep that in mind, would it be prudent to replace the magneto wires with shielded cable as well (before the coil) and earth the shield on one end, or do you think it would not make much difference. I believe that most of the noise is from the ht lead after the coil. Do you have any ideas on shielding that lead as I can't replace the cable, it is a sealed unit on the coil. Once again Mike, I really appreciate the help, and I'm learning a lot in the process......
9  Using Arduino / Motors, Mechanics, and Power / Re: Magneto interference with arduino on: February 24, 2013, 03:36:41 am
Thanks heaps for your help, I'm going to give it a go. I'll post here to let you know on progress, but it might take a while as I don't get much time to play with it.
10  Using Arduino / Motors, Mechanics, and Power / Re: L293D Getting Really Hot, Really Fast on: February 24, 2013, 02:51:11 am
I don't think it would matter too much if you did or didn't connect the sink to the pins, I think the idea behind the data sheet specs is to show that it is the common ground and, as some heatsinks need to be earthed to stop noise, and sometimes the sink that is used is the ground, like the side of an allum enclosure, it's showing it can have a ground link there to help prevent ground loops or just bad earth.
11  Using Arduino / Motors, Mechanics, and Power / Re: L293D Getting Really Hot, Really Fast on: February 24, 2013, 01:52:00 am
Jimbo, I just saw the link above for the board, I don't see any probs heat sinking these chips, if it was me, I would get an allum sink the right size to go across the three processors and use heatsink compound to "glue" it on. Ok it's not ideal, but it would be better than nothing.
12  Using Arduino / Motors, Mechanics, and Power / Re: L293D Getting Really Hot, Really Fast on: February 24, 2013, 01:26:53 am
That's always the fun part, as I have said before, I'm not farmilliar with this board, but I know that in some cases you have to get really creative. I have had to mill up my own aluminum sinks specially shaped and use a bit more thermal paste than I would like, but it works. Mostly tho, if the board was supposed to have a heatsink, it normally has some kind of provision for mounting it, even if that is just a small flat surface to "glue" it on the chip.
13  Using Arduino / Motors, Mechanics, and Power / Re: VFD - anyone any experiences or hints? on: February 24, 2013, 01:10:13 am
Don't know if it is of any help now as this is an old thread, but I have used ebay for vfd's and found the prices not too bad. The last one I bought was around the size you wanted and only cost me $140aus brand new. I know you did not want to buy one based on price, but I've found that this is the easiest solution and most vfd's have some sort of serial port coms which you can interface with arduino.
14  Using Arduino / Motors, Mechanics, and Power / Re: Magneto interference with arduino on: February 24, 2013, 12:56:58 am
Sorry, I was asking if I should decouple the power supply on the arduino as well as try to somehow decouple the magneto as well ( it has a low volt magneto and a seperate coil), or just the arduino supply would suffice? This decoupling stuff seems pretty in depth, am I going to hurt anything if I just use the trial and error method?
15  Using Arduino / Motors, Mechanics, and Power / Re: L293D Getting Really Hot, Really Fast on: February 24, 2013, 12:52:12 am
Sorry, I was not saying it would, I'm not familiar with the L293D. I have however, been caught out by the lack of heatsinks in cases before. Even some of the high end vfd boards I use for CNC conversions come without the heatsinks which is kind of frustrating, but sometimes it can be handy as you can mount them all on a tunnel type heatsink with a pc fan blowing down it.
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