2021-06-16, 05:31 PM
(This post was last modified: 2021-06-16, 07:27 PM by baltika_no_9.)
(2021-06-16, 02:47 PM)SCarns Wrote: That is correct. The VDO senders are new, as the old ones fail. Yes, a center wire and a ground on them. Keeping the gauges would be preferable.
OK thanks
In that case you are probably never going to see the full 12V at that sender connection but quite how close it would get entirely depends on how VDO have designed it. I think if it were me I'd measure the voltage at the sender (sense connection to ground connection) when the tank is full and when it's empty (or lift the sensor and physically move the actuator arm from one limit to the other). That gives you the voltage range you'd want to measure with your ADC. You may find it is within the capabilities of say the ADS1115 without the need for a resistive network to reduce it. The ADS1115 can do approximately 0-6V. Probably worth recording the resistance at both points too just for confirmation. Disconnect one or both connectors for this of course.
Anyway only once you know the voltage range can you decide on the resistors.
You'd probably want to keep the resistor values quite big (while maintaining the correct ratio) as adding them might well change the characteristics of the existing circuit and when the tank is actually full the VDO gauge might show something slightly different. Unfortunately unless you can delve inside the VDO gauge itself and see what's in there you can't be specific on what, if any, effect there may be. You'll just have empirical evidence. Ideally of course you'd need the variable resistance across the sender to be a close as possible to the 0Ω to 190Ω (or whatever it happens to be) even when any resistive network is placed in parallel with it.