G+_James Hughes Posted December 20, 2017 Share Posted December 20, 2017 Here I go again... This is the umpteenth time I've changed the set-up for a project that I've been working on. I'm using a potentiometer to control the direction and movement of a stepper motor. This is done with an Arduino Nano, an A4988 stepper controller, and a 10k pot. The picture of the Boost SU Converter is what is being represented by the two vertical lines on the right of the Fritzing diagram. I had this set up working pretty much wired as shown and now for the life of me I can't get it to work. The power in is 5v from a micro usb so the voltage to the power rail is 5v. The output for the motor is 10v. It's acting as if I have some wires crossed which I'm sure I don't. But when I check the voltage I'm getting half of what I should be getting on the 5v side and both sides are about the same. Any thoughts would be appreciated. Link to comment Share on other sites More sharing options...
G+_John Sullivan Posted December 21, 2017 Share Posted December 21, 2017 You said "I'm getting half of what I should be getting on the 5v side and both sides are about the same." Where are you measuring this exactly? on the in and out of the boost converter? and you're getting what, about 2.5 v? Link to comment Share on other sites More sharing options...
G+_Charlie King Posted December 21, 2017 Share Posted December 21, 2017 Is B+ 5 VDC? Link to comment Share on other sites More sharing options...
G+_James Hughes Posted December 21, 2017 Author Share Posted December 21, 2017 cosmic Ray yes, I'm measuring on the converter and yes, about 2.5 volts. I did some reading on the questions that were answered and they said that the USB and the Up Converted side are not isolated if that makes any difference. Link to comment Share on other sites More sharing options...
G+_John Sullivan Posted December 21, 2017 Share Posted December 21, 2017 If you're supplying 5v to the converter, but are only measuring half of that at the input connections, and also the same voltage at the output, my first guess would be that it's shorted out, and I would replace it. But if you want to test it out, disconnect power and then disconnect everything downstream from the converter. Connect a resistor across the converter output connections, re-connect power and read the voltages. If the voltages return to normal, then the problem is downstream (something drawing too much current) Link to comment Share on other sites More sharing options...
G+_James Hughes Posted December 21, 2017 Author Share Posted December 21, 2017 Charlie King The input is either USB (5 volts DC) or 2 - 24 volts DC on the pins and the output can be anywhere from 5 to 28 volts DC. The A4988 needs at least 8 volts on the motor input. There is something definitely wrong because both the coil on the converter and the heat sync on the A4988 get really hot. At first I thought I might have had the polarity on my wires the wrong way around but I've double and triple checked. Link to comment Share on other sites More sharing options...
G+_James Hughes Posted December 21, 2017 Author Share Posted December 21, 2017 Tomorrow I'm going to try powering the motor side of the A4988 with a 12 volt battery and supplying the 5 volt logic power from the USB to see if isolating the power makes any difference. If it does I'll have to figure out a way to isolate the power on the converter. Link to comment Share on other sites More sharing options...
G+_James Hughes Posted December 21, 2017 Author Share Posted December 21, 2017 cosmic Ray Thanks for the input. It definitely appears that something is shorting out. I'll test it with a resistor on the output as I've tested it without one (disconnected from everything) and it works fine. Link to comment Share on other sites More sharing options...
G+_James Hughes Posted December 21, 2017 Author Share Posted December 21, 2017 cosmic Ray so it appears that both the high and low positive voltage sides are connected. I tested them with my multimeter to confirm this (pulled one straight out of the packaging too). I'm not sure how you can supply 3 - 5.5v for the logic and 8 - 35v for the motor when they are connected. I've looked at a bunch of different wiring diagrams on google and they all are the same. I even put a diode on the high side to prevent back voltage which had some positive effect but still can't get this going. #reallyfrustrated Link to comment Share on other sites More sharing options...
G+_John Sullivan Posted December 22, 2017 Share Posted December 22, 2017 James Hughes the "high and low positive voltage sides" of what? the up converter? If you tested them with an ohmmeter (multimeter), that is not a valid test. These circuits are too complex internally for that. You need to test the up converter under load (like a resistor) to verify that it is putting out the proper voltage Once you've established that, you connect it back into your circuit and read the "high" voltage at the input to the A4988 where you have the capacitor connected. Once you get sufficient voltage at that point, if it still does not work, you need to verify what your Arduino is outputting, possibly by using its serial monitor. Link to comment Share on other sites More sharing options...
G+_James Hughes Posted December 22, 2017 Author Share Posted December 22, 2017 cosmic Ray Sorry I wasn't clear. I was referring to the A4988. I checked for continuity with my multimeter. I did check the up converter with a 4.7k resistor and got the 10+ volts I was expecting. I'm not sure what I'm doing wrong. I did have success early in the week so I soldered up a proto board and that's when things went south. Link to comment Share on other sites More sharing options...
G+_John Sullivan Posted December 22, 2017 Share Posted December 22, 2017 James Hughes Again, using a multimeter in this manner is not a valid test. What you are doing is applying a voltage across the two positive connections (low voltage in and high voltage in), instead of positive connection to negative connection. These microcircuits are complex inside, and you cannot tell whether it is reacting properly or not. What you have proven is that the up converter is working correctly. Now that you know you are getting a good 10v when applied across a known fixed load (the resistor), if you apply that voltage to the A4988 and then read the voltage and it is much less, then something is wrong inside the A4988. What would draw down the voltage is a high current load (a short or partial short) If you have the stepper motor attached, double check that you do not have two of the four wires reversed. I know you've checked them already, but check again. Link to comment Share on other sites More sharing options...
G+_John Sullivan Posted December 22, 2017 Share Posted December 22, 2017 James Hughes You probably have a good circuit diagram already, but here's the one I found, just in case: https://www.pololu.com/product/1182 (scroll way down on the page) Link to comment Share on other sites More sharing options...
G+_James Hughes Posted December 22, 2017 Author Share Posted December 22, 2017 cosmic Ray Yes, that's the circuit diagram I've been referring to for mine. Link to comment Share on other sites More sharing options...
G+_Jason Brown Posted December 23, 2017 Share Posted December 23, 2017 Everyone needs a plan they can deviate from. My favorite projects are the ones I came up with after hitting a dead end from another one. Link to comment Share on other sites More sharing options...
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