We have to interface with the device that is expecting a chain of 34 Ohm resistors with switches connected to the input pins as shown below. There is no information on the internal schematics of the device, but there is 10V present on the open circuit and when shorted the current is limited to 5mA. The documentation mentions "maximum input voltage 34V", which is weird, since we are not expected to _supply_ voltage to those pins.

[![enter image description here][1]][1]

My first thought was to simply emulate the suggested circuit with analog switches (like [ADG715][2]) and a bunch of resistors. Then I thought of digital potentiometers (like [AD5254][3]), that do not need resistors.

The problem, however, is that all these chips have analog voltage limits pretty close to their digital supply lines. So, it seems I need either a way to add high voltage-tolerant output stage to digital pot, or use completely different approach, like DAC + VCR (voltage controlled resistor). Unfortunately analog circuits are still my weak spot, not sure I can design FET-based linear VCR properly.

Any other options I have missed?


  [1]: https://i.sstatic.net/urahR.png
  [2]: https://www.analog.com/media/en/technical-documentation/data-sheets/ADG714_715.pdf
  [3]: https://www.analog.com/media/en/technical-documentation/data-sheets/AD5253_5254.pdf