- Fri Apr 22, 2022 12:37 pm
#56618
Hello All,
TLDR: Can I control an old style CLT gauge with an unused PWM output from Speedy?
Me again, back with some more musings on how to do something I should already know!
The Stag has it's original CLT gauge, which is effectively an ammeter, where the current that flows through the gauge is dictated by the resistance of the sender.
Now I've replaced the sender (original 1 wire to new 2 wire bosch type), I need to interface the gauge. Ideally I'd rather not have 2 senders on the engine.
My first thought was to use a digital potentiometer on a separate microcontroller to replicate the resistance of the old sender (which is similar to bosch, ~2k5 cold and ~150r hot), however this would mean around 100mA to cope with, which is more than I could find a dig. potentiometer to handle.
So my next thought is to utilise an unused mosfet (e.g. idle output) to PWM ground the gauge sender, through a current limiting resistor, to drive the gauge. This can be linked to the coolant temperature the Speedy is measuring, and so would be calibratable through TS to get the gauge to read correctly.
The gauge is fed through a 10V voltage regulator (which I've replaced with a modern chip rather than the original switching type).
My actual question: Would this/Can this work?
I think max average current through the mosfet would be (10V / 60r) =~ 160mA, if I had a 60r inline resistor and had the DC at 100%
Cheers in advance for anyone's thoughts!
TLDR: Can I control an old style CLT gauge with an unused PWM output from Speedy?
Me again, back with some more musings on how to do something I should already know!
The Stag has it's original CLT gauge, which is effectively an ammeter, where the current that flows through the gauge is dictated by the resistance of the sender.
Now I've replaced the sender (original 1 wire to new 2 wire bosch type), I need to interface the gauge. Ideally I'd rather not have 2 senders on the engine.
My first thought was to use a digital potentiometer on a separate microcontroller to replicate the resistance of the old sender (which is similar to bosch, ~2k5 cold and ~150r hot), however this would mean around 100mA to cope with, which is more than I could find a dig. potentiometer to handle.
So my next thought is to utilise an unused mosfet (e.g. idle output) to PWM ground the gauge sender, through a current limiting resistor, to drive the gauge. This can be linked to the coolant temperature the Speedy is measuring, and so would be calibratable through TS to get the gauge to read correctly.
The gauge is fed through a 10V voltage regulator (which I've replaced with a modern chip rather than the original switching type).
My actual question: Would this/Can this work?
I think max average current through the mosfet would be (10V / 60r) =~ 160mA, if I had a 60r inline resistor and had the DC at 100%
Cheers in advance for anyone's thoughts!