I am looking for ideas to implement fail-safe function in joystick control box. At present, the 5V joystick HF11S10 is connected to STM32 ADC inputs via simple 5.1k:9.1k divider. We are revising the schematics to conform to all requirements for powered medical devices, so we would like to be able to detect the disconnected or damaged wiring. With current schematics disconnected joystick results in valid 0V signal. In terms of application logic it is identical to “full reverse speed” input, which is extremely dangerous.
Note that we already solved this problem in the future projects by ordering joysticks with limited output range 0.25V-4.75V, which makes 0V signal invalid. Another possibility is to use joystick variants with digital interface available from manufacturer. However we do have a stock of old devices, and considering their price we’d very much like to find a simple solution that allows us to use them safely.
Important characteristics from datasheet:
- Ratiometric output voltage 0V-5V
- Output current 8 mA
- Output load min 1 k
- Output impedance 2 Ohm
- Supply voltage range 5VDC ±0.01VDC
Also, just in case, there are couple digital inputs available and by moving things around I might be able to free one analog input.