I am a graduate student with little coding and small circuitry experience but am eagerly learning.
Project: Use 3 FSRs and create a glove that can be used to analyze forces on the thumb, middle, and pinky fingers. This will hopefully be used for a rock climber to see how they load their fingers while climbing. Data needs to be collected from each FSR individually while being stored on a Micro SD card.
Currently i am able to set up the 3FSRs in parallel and have them all give a reading. The image I've attached is the diagram i refrenced to connect all 3. I have each sensor going to a designated analog input pin each with their own 1M resistor. Since they all come from the same 5V slot on the arduino if i press on 1 i get a ghost signal on the others.
Id like help with attaching a Micro SD card for data collection and storage. Ive spoken with someone who says i may need a step down voltage regulator to hold each FSR at 5V.
I have the Load cell amplifier listed since my professor recommended me to try and work with an amplifier to get a better and more clear signal.
jdmira:
Since they all come from the same 5V slot on the arduino if i press on 1 i get a ghost signal on the others.
No, NOT because the pull up comes from the same 5volt supply, but because of the high pull up/down resistance.
The Arduino has only one A/D.
The analogue inputs are switched in turn, with the internal multiplexer, to that single A/D converter.
If the voltage sources are not 'solid' enough (low impedance, <=10k), then cross-talk between channels will occur.
The solution could be buffer op-amps between FSR and analogue inputs, like shown in the FSR datasheet.
Or... simply a 100n cap from each analogue input to ground, close to the Arduino.
1Megohm pull down seems very high, and could only be ok for small forces.
Might have to reduce that (10-100k), so an average force produces an A/D value of about 512.
I would use the FSR between pin and ground, and a pull up resistor between pin and 5volt.
That could make your glove 'safer' from accidentally shorting 5volt to ground.
It will 'reverse' A/D readings, but that can be easily fixed in code.
Leo..
Internal pull up is fine for things like switches.
Not sure if it's a good idea to use it for exact measurements and/or compare pressure between the three channels, since the pull up value is not well defined in the datasheet.
Leo..
Working with my friend we used a Pololu 5V 600mA step-down voltage regulator for each sensor. This allowed each sensor to give off their own individual readings. I did some research on the serial plotter in the arduino program. Most of what i have seen says it won't show different readings at the same time.
Would i be able to code the arduino to send the voltage readings to Qwiic_openlog micro sd and store each one individually? I can attach the Qwiic_openlog to the Arduino through pins SCL,SDA, and 3.3v. I know there is a connector i can buy to attach to the ICSP but is that necessary with the above pins connected?
As of right now with COVID-19 moving everything to online classes. He has given me a bunch of leeway with the project. As long as i can get the sensors to give reading to the micro sd ill be alright.
jdmira:
Working with my friend we used a Pololu 5V 600mA step-down voltage regulator for each sensor.
That doesn't sound right.
If you power a FSR from a different source than VCC of the Arduino, then you loose ratiometric relationship between the sensor and the A/D. Meaning the sensor output depends now on three things instead of one.
Leo..
