1 Topic by Claghorn

  • Claghorn
  • Member
  • Offline
  • From: Delray Beach, FL
  • Registered: 2012-10-22
  • Posts: 730

Topic: Interfacing Force Sensitive Resistor to Printrboard?

I'm looking at interfacing a force sensitive resistor to one of the available analog inputs on my printrboard to see if I can successfully detect the nozzle touching the print bed (early experiments with an ohm meter were promising). I'm wondering if the same sort of circuit used for the thermistors would work with the FSR as well?

I also see the thermistor circuits have a capacitor labeled as 10μF that appears to be a teensy little surface mount thing on the board. Out of curiosity, what the heck kind of capacitor can provide 10μF in such a small package?

Claghorn's Website

2 Reply by adrian (edited by adrian 2013-12-28 08:22:36)

  • adrian
  • Member
  • Offline
  • From: Canberra, Australia
  • Registered: 2013-01-15
  • Posts: 1,623

Re: Interfacing Force Sensitive Resistor to Printrboard?

It's a 10uf ceramic... you're thinking electrolytic which are usually bigger but are also incredibly small these days.. but yes it is an 0603 or 0402 (depending on which printrboard it is) 10uf ceramic.... anyway..

The thermistors are just a simple voltage divider circuit using the thermistor as R1 in the divider and the cap's just a filter to prevent transients as the 5v line sags and spikes...

You can therefore use the force res as R1 in the divider ladder, or..... just use one of the many other analogue pins available. .. if you wish to remain compatible so to speak with mainline firmware et al, don't re purpose the existing pins....

3 Reply by Claghorn

  • Claghorn
  • Member
  • Offline
  • From: Delray Beach, FL
  • Registered: 2012-10-22
  • Posts: 730

Re: Interfacing Force Sensitive Resistor to Printrboard?

Wow. I looked up ceramic caps on digikey, and there they are with a max thickness of 0.5mm. Learn something every day. Thanks. I guess I probably don't need a capacitor to make this work (at least to experiment, anyway).  Detecting the nozzle touching the print bed seems like it will require noticing a fairly sudden change in resistance that stays changed for a while. Apparently the resistance will wander gradually due to temperature and other factors, so I can't make any absolute values mean anything anyway, and spikes should get averaged out (that's the theory, anyway).

Claghorn's Website