Help -> generate 0 - 50mV dc with arduino

Hi phoenixcomm ,

Please can you a bit explain your needing, your application? e.g. with a photo, or drawing?

0...50mV output voltage can earn a big problem.

Normally under 0,9 V the output signal is logical LOW. Under that the voltages are not defined because at this area you have noise, GND bouncing, threshold and so on.

Please read in the data sheet, page 385, in the chapter 32.7 "Pin driver strength".

You will find the diagram fig. 32-22 I/O Pin output voltage vs. sink current (VCC = 3V). which says that if you sink the pin with 3mA the output voltage will rise up to 0.1V.

And so on,,,, with a 20mA load gets rising up to 0.7 V (25°C; 0.85V 85°C).

Similar you have this as well with the 5V source.

So direct source like with a PWM or so, does not functioning, I think.

-> With a PWM the output voltage can very big vary if you have not a right limitation. Once toggling the frequency or pulse width the output voltage grows up.

What I can think about (I don't know your appl. "for a meter, you said"), if you make a virtual GND with an OPAMP (driven by the I/O pin), and with a DAC trim it with the offset to your 50mV.

Must the 50mV be switch-on able?

Best Regards

Gerald

---

Hi phoenixcomm ,

Please can you a bit explain your needing, your application? e.g. with a photo, or drawing?

0...50mV output voltage can earn a big problem.

Normally under 0,9 V the output signal is logical LOW. Under that the voltages are not defined because at this area you have noise, GND bouncing, threshold and so on.

Please read in the data sheet, page 385, in the chapter 32.7 "Pin driver strength".

You will find the diagram fig. 32-22 I/O Pin output voltage vs. sink current (VCC = 3V). which says that if you sink the pin with 3mA the output voltage will rise up to 0.1V.

And so on,,,, with a 20mA load gets rising up to 0.7 V (25°C; 0.85V 85°C).

Similar you have this as well with the 5V source.

So direct source like with a PWM or so, does not functioning, I think.

-> With a PWM the output voltage can very big vary if you have not a right limitation. Once toggling the frequency or pulse width the output voltage grows up.

What I can think about (I don't know your appl. "for a meter, you said"), if you make a virtual GND with an OPAMP (driven by the I/O pin), and with a DAC trim it with the offset to your 50mV.

Must the 50mV be switch-on able?

Best Regards

Gerald

---

geralds Hi, basically i need to emulate a high current shunt, my load meter has 50mV fullscale defection.

there are pics and info about the load meter here.

grr. could not load my tiff image. so basically you have a generator with - to ground and + to the shunt, on one side of the shunt run a wire to the meter, and another to the LOAD. the other side of the shunt one of the wires goes to the loads ground the other wire goes to the - terminal on the meter.

I just had a senior moment I converted the image from tiff to jpg. :)

I want to do this with the PCM output from the Arduino Max. The meter has 16 tics, so I really should hit all of them + the ones in-between as well

I need to spend as little money as possible, or, as cheaply as I can get away with.

thanks again.

~Cris.

BTW since the meter is messuring Load which is just a percent of Total load so arbitry numbers are fine.