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Incorporating NodeMCU ESP8266 senders
#11
(2021-06-10, 06:20 PM)SCarns Wrote:
(2021-06-10, 04:23 PM)affinite Wrote: Im not an electronics expert (so please double check this) but I would have thought is would work if you simply created a resistance bridge to reduce the full-scale voltage from the sender to 3.3v then its just a case of calibrating the ADS1115 in ESPEASY.
The bridge would comprise Ground - 1kOhm -1 x 3kOhm - Attach to tank sender.(max 12v).
I would have thought this would work in parallel with the VDO gauges.

Thanks affinite!

I am sure it can work, I just don't (yet) have the knowledge to pull it off. This is a big help, though. Give me something to research further until someone else here says, "Hey dummy, just use 'X', attach it to 'Y' and plug it into 'Z'"!

Steve

The proposed resistance ladder makes sense if the tank sender ever saw 12V but I doubt it ever would yet I don't know your particular set up.
Does the sender unit itself have just two terminals sender and ground? Am I right that you are planning to retain the VDO gauges themselves as they work ok?
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#12
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.
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#13
(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.
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#14
(2021-06-16, 05:31 PM)baltika_no_9 Wrote:
(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.

Excellent info! I do know the VDO's have a different resistance - mine are 0Ω for empty and 90Ω for full. And there is a tank right under my RPi install, so I think I'll check the voltages and give this a try.

Thanks for the info baltika#9! Big help.

Steve

One more thing... I think "Triangle Tank Calculator" and other plugin/add-ons in SK will actually help make this more accurate than the old gauges. As stated, they aren't very accurate and fluctuate a lot with subtle changes in voltage.
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#15
That's a very good point, susceptibility to changes in the 12V rail is a feature of systems that rely on voltage measurement. They do assume a stable supply which is of course not the case.
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#16
I was able to put a volt meter on my senders tonight and was surprised to discover affinite was indeed correct regarding voltages at the tank senders. The port fuel tank is about half full (by depth) and measures 3.2 volts. The starboard tank 2/3rds full and measures 2.8 volts. Obviously that suggests an empty tank would have a voltage in the neighborhood of about 6.5 volts, which is above what the ADS1115 can handle.

I'm still not exactly clear. Do I still need a 1k resistor in line of the positive side? Or would something smaller work. Do I need a divider? And if so, with these small differences in voltage, what would the resistors be?

I've learned a lot so far, but I'm not ready to start frying ADS1115s just to test ideas. Id kind of would rather have it right to begin with.
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