How can I properly source a varying negative voltage using an Arduino? I would like to use the 5V supply pin on the Arduino, scale it down (dynamically) to an appropriate voltage, and convert it to a negative voltage to be used as a negative supply source.
I've seen posts that use the ICL7660 negative voltage converter to supply a negative voltage. I also would like to get as close to 0 volts (a very high negative voltage, ex: -0.1V) as possible.
From my knowledge, there are two ways of doing this:
First Method:
- Scale 5V input voltage using digital potentiometer
- Use some IC to convert output voltage of digital potentiometer to a negative voltage
Second Method:
- Convert 5V input voltage to a -5V using some IC
- Scale -5V using a digital potentiometer
Are there any downsides of sourcing the FSR with either of these two methods? What specific components would you recommend? I have a MCP4231 digital pot (but won't work for second method since it doesn't take negative voltage).
The end goal is to be able to source a varying negative voltage (controlled by a digital pot that I can alter using software) without any extra batteries. I would also like to get a good amount of variation between -0.1V and -5V.
I am trying to use the negative voltage to source the Flexiforce force sensitive resistor here (the Vt in the picture below):
Also any advice for a different electronic frontend circuit that provides similar control of the dynamic force range would be helpful!
EDIT
Per @DrFriedParts advice, I have used his circuit to eliminate using a negative voltage source altogether. However, when simulating the circuit and implementing it, I don't seem to get an output different than 5V.
Here is a snapshot of the circuit:
The output is always 5V, no matter what values I change for Rs (the sensor) and Rf (feedback resistor). Am I doing something wrong? Shouldn't I apply a bias voltage much lower than 5V (like 0.5V) so the output will be from 0.5V to 5V?