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Thanks Bob & Steve
"a gain of 1", that is what I thought. Im not sure why my local electronics guy has changed the circuit that I gave him that Chris originally devised for me, but that now confirms my thoughts. Im not sure about the negative feedback (in fact I am not sure what you mean by that). Its the gain I was worried about." Will the negative feedback be a problem ?
Thanks
Justin
"a gain of 1", that is what I thought. Im not sure why my local electronics guy has changed the circuit that I gave him that Chris originally devised for me, but that now confirms my thoughts. Im not sure about the negative feedback (in fact I am not sure what you mean by that). Its the gain I was worried about." Will the negative feedback be a problem ?
Thanks
Justin
Hi Bob
The output from the Pic is approx 0 - 5V. The original circuit was tocontrol a brush less motor controller that had a 0 - 5 V input. However when I eventually decided on the brush less controller its input needed to be 0 - 10V, so the fix was to use an op amp with a gain of 2.
I gave the schematic that Chris designed for me to a local company to produce the boards but they say this config shown here gives a gain of 2 but my workings say the gain is 1 and therefore pointless in this application.
Am I correct?
Thanks
Justin
The output from the Pic is approx 0 - 5V. The original circuit was tocontrol a brush less motor controller that had a 0 - 5 V input. However when I eventually decided on the brush less controller its input needed to be 0 - 10V, so the fix was to use an op amp with a gain of 2.
I gave the schematic that Chris designed for me to a local company to produce the boards but they say this config shown here gives a gain of 2 but my workings say the gain is 1 and therefore pointless in this application.
Am I correct?
Thanks
Justin
Justin,
The gain of your opamp circuit is indeed 2, but you have taken the output from the PIC and put it through a voltage divider that halves it, so the output of the op amp is the same as the output from the PIC. Is this a DAC output? I did not know there were any small PICs with a DAC? And why do you have a .1uF capacitor shorting the output? This makes a low pass filter controlled by the output impedance of the PIC pin, is this your intention?
Bob
The gain of your opamp circuit is indeed 2, but you have taken the output from the PIC and put it through a voltage divider that halves it, so the output of the op amp is the same as the output from the PIC. Is this a DAC output? I did not know there were any small PICs with a DAC? And why do you have a .1uF capacitor shorting the output? This makes a low pass filter controlled by the output impedance of the PIC pin, is this your intention?
Bob
Hi Bob
You might remember the thread in the Summer that you made some valuable contributions to that helped me allot. Chris AKA "CDRIVE" developed a circuit for me and this is the result of that circuit. I am still working on it. I have been unable to make contact with Chris for help but here is the link to the thread to remind you,
I combined the circuit at this link
https://www.electronicspoint.com/digital-pot-setup-t248126p11.html#post1469754
with the circuit at this link
https://www.electronicspoint.com/digital-pot-setup-t248126p17.html#post1472431
I am still very novice, but I have worked out today that the voltage divider is halving the input. Chris probably thought that when I combined the circuits I would have altered them in some way,,however I simply added one to the other as I needed the output from the DAC to be 0 - 10V. Chris designed the circuit with the 0 - 5V output in mind and I threw the spanner in the works towards the end that I needed 0 - 10V as I ended up using a different controller to that which I stated I would use initially.
Justin
You might remember the thread in the Summer that you made some valuable contributions to that helped me allot. Chris AKA "CDRIVE" developed a circuit for me and this is the result of that circuit. I am still working on it. I have been unable to make contact with Chris for help but here is the link to the thread to remind you,
I combined the circuit at this link
https://www.electronicspoint.com/digital-pot-setup-t248126p11.html#post1469754
with the circuit at this link
https://www.electronicspoint.com/digital-pot-setup-t248126p17.html#post1472431
I am still very novice, but I have worked out today that the voltage divider is halving the input. Chris probably thought that when I combined the circuits I would have altered them in some way,,however I simply added one to the other as I needed the output from the DAC to be 0 - 10V. Chris designed the circuit with the 0 - 5V output in mind and I threw the spanner in the works towards the end that I needed 0 - 10V as I ended up using a different controller to that which I stated I would use initially.
Justin
I believe it this one :- PIC12(L)F1840
Here is the link to the PICAXE site that refers to this chip:
http://www.picaxe.com/What-is-PICAXE/PICAXE-Chip-Labels/
Justin
Here is the link to the PICAXE site that refers to this chip:
http://www.picaxe.com/What-is-PICAXE/PICAXE-Chip-Labels/
Justin
Returning to your question, to get a gain of two, eliminate the capacitor and two resitors in the circuit connecting the DAC to the + input. Just connect the pin directly to the + pin.
Not sure why the capacitor was there, if you want to slow the response to changes, you could place a resistor from the DAC output to the + pin and a capacitor from there to ground, forming a low-pass filter.
Bob
Not sure why the capacitor was there, if you want to slow the response to changes, you could place a resistor from the DAC output to the + pin and a capacitor from there to ground, forming a low-pass filter.
Bob
Thanks Bob for looking at this for me. You have now confirmed exactly what the guy said who was looking at the circuit for me. As you can see, he has placed the word omit next to the resistor.
I spoke to him yesterday and he basically said what you have said. I have just ordered 30 of these PCBs with surface mounted components as its to be on a very narrow PCB. I was worried about the outlay, when I was unsure about the circuit.
I should have trusted my local guy as he has a good reputation and now you have backed it up.
Thanks
Justin
I spoke to him yesterday and he basically said what you have said. I have just ordered 30 of these PCBs with surface mounted components as its to be on a very narrow PCB. I was worried about the outlay, when I was unsure about the circuit.
I should have trusted my local guy as he has a good reputation and now you have backed it up.
Thanks
Justin
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