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PSoC 5, 3 & 1 MCU

Anonymous
Not applicable

Hi Guys,

   

I'm trying to drive a Pololu JRK motor controller, but I think the VDAC's on the PSoC 5LP Kit does not supply enough current to do so.

I get a perfect reading off my VDAC with an Oscilloscope before I connect the JRK Controller, but the voltage will not drop below 1.9V after connecting it. The JRK works fine directly from a Potentiometer.

I want to put an op-amp in between the PSoC and the controller to buffer this, but I want to lose as little resolution and keep as much accuracy in the output as possible.

   

I need a DIL package so I can strip-board with.

I'm struggling to find a Op-Amp that ticks all the boxes, and I don't want to order some only to find out they're not suitable a few weeks before the deadline for my project when they arrive. 😞

I don't have any experience using a buffer like this, so am unsure where to turn.

Any help is much appreciated 🙂

   

Thanks,
Tommy

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1 Solution
Honored Contributor II

Here is a program example for you to study.  Output current 10ma.

View solution in original post

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7 Replies
Anonymous
Not applicable

You can try using one op-amp on the PSoC 5LP in unity gain configuration. The DAC has an output resistance of 4 or 16k, so it cannot supply more than a fraction of a mA. The op-amp can source or sink 10mA.

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Anonymous
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I have actually already tried this, which perhaps I should have mentioned.

Unfortunately, when I connect it it still won't let the voltage go below 1.9 when connected, but still outputs 0V without connecting to JRK.

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Honored Contributor II

If even with a buffer on the DAC you cannot get the signal _below_ a certain value something is wrong with your circuit. Probably there is something else driving that signal / wire. Check your PCB and everything you have connected. Note that the OpAmp in the PSoC cannot sink an infinite amount of current.

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Anonymous
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        I'm driving the Pollolu JRK straight from the PSOC via breadboard, and they're running from the same power source. It's connected straight to the Analog RX on the JRK and it works fine using a Pot instead. 😞   
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Honored Contributor II

My best guess is that for some reason the motor driver is not in analog input mode. Can you measure what current is flowing between the PSoC output and the JRK input? It should be really low, anything else indicates wrong wiring / configuration of some kind.

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Anonymous
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I can confirm HLIs guess!
Just have checked on my board and the current in analog mode is < 1mA.

   

Double check your config and measure one more time the current  😉

   

All the Best
Frank

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Honored Contributor II

Here is a program example for you to study.  Output current 10ma.

View solution in original post

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