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Is this circuit incorrect

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yngndrw

New Member
Hi,

I just wanted to check that this configuration is incorrect. It is part of a stepper motor driver which I bought and I've traced the problem back to this. It seems that the opto-isolator's output is the wrong way around but I thought it was best to double check if this makes any kind of sense.

http://yngndrw.hostilezone.net/uploads/Stepper Driver Fail.png

At point A, I measure a high level signal to be 5V and a low level signal to be 1.7V. This means that the schmitt inverter never outputs a high signal.

Thanks,
-Andrew.
 

Hero999

Banned
It's the wrong way round and it also requires a pull-down resistor.
 

yngndrw

New Member
Okay that's perfect, now I can ask for a refund on it now that I've double checked that.

Thank you for your help Hero999 and audioguru.
 

Torben

Well-Known Member
Okay that's perfect, now I can ask for a refund on it now that I've double checked that.

Thank you for your help Hero999 and audioguru.
Now that you know what the problem is and what the fix is, why not just fix it?


Torben
 

yngndrw

New Member
Well I spent a total of $155 for a 5 axis stepper motor driver - I could get the same for less but thought that this one looked better. When I spend that amount I want a product that works, I shouldn't have to make messy fixes just because the original designer didn't test his products.

That and as it's a PCB the fix would turn out quite messy. I'd have to bend up two of the legs and use a piece of wire to jump them to the correct holes.
 
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Torben

Well-Known Member
Well I spent a total of $155 for a 5 axis stepper motor driver - I could get the same for less but thought that this one looked better. When I spend that amount I want a product that works, I shouldn't have to make messy fixes just because the original designer didn't test his products.

That and as it's a PCB the fix would turn out quite messy. I'd have to bend up two of the legs and use a piece of wire to jump them to the correct holes.
Fair enough. :) What make and model is the unit?


Torben
 

yngndrw

New Member
It's made by Univelop:
5 AXIS CNC STEP MOTOR DRIVER 5 AXIS CNC STEP MOTOR DRIVER [CNC5AIXS55] - $149.99 : CNC Driver ARM Ulink 5-axis BDM Keil Mill - CNCGeeker.com Univelop Tech. LLC, CNC
Although I bought mine over Ebay.

It's a nice idea to have the drivers split from the break out board, however the implementation isn't very good at all. The heatsink is near useless unless you have a large fan. They mention "Full adjustable stepper motor current" however they forget to mention that you have to de-solder a resistor to do so - Not quite as adjustable as I'd expect. The PCBs have some very thin traces which are meant to carry the full Motor current. The PCBs also have some traces which don't go anywhere - Which seems a bit lazy to me.

I've put up with all of these but this last error is just too much for me. Having said all of this, it does work quite well in the one direction that works.

Oh and I forgot to mention, I blew up one of the driver ICs while I was trying to find out what was stopping it from reversing. I thought it wouldn't be a problem as I'll just get a replacement IC, however the seller would only sell me a full replacement board for $40. (I turned him down on that offer, as I found the IC on CNCZone for £3.30 and that's probably much higher than you can get it for elsewhere.)
 
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fernando_g

New Member
Well I spent a total of $155 for a 5 axis stepper motor driver - I could get the same for less but thought that this one looked better. When I spend that amount I want a product that works, I shouldn't have to make messy fixes just because the original designer didn't test his products.
Unfortunately, this is not an isolated case, a friend of mine bought a high power white LED supply on EBAY, only to have it blow in his face. It turns out that the silkscreen for the freewheeling diode was backwards!!
 

yngndrw

New Member
Well that sucks, I hope Ebay sorted it out for him and he got his money back. Then again, you always still seem to loose out with Ebay's buyer protection - Not getting the postage costs back or something like that.
 

Hero999

Banned
I understand now that you need a pull-up resistor, not a pull down resistor. The upside down transistor had me confused.
 
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