Output to AFR gauge - possible / any ideas on how

dr_jones
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Re: Output to AFR gauge - possible / any ideas on how

Post by dr_jones »

Thanks Tim!!

That's a great help - the 'View - Customising Options' was the part of the jigsaw I was missing.

The gauges inputs are specced as 0v = 7.35 A/F and 5v = 22.39 - So I guess I'd need to use an IGN output to drive it (they seem to be the only 5v outputs) - however this brings with it a concern - there is a note there in the S6Plus pinouts and wiring guide about danger of damaging the ECU if the IGN outputs are directly connected to low resistance but nothing as far as I can see about what constitutes a low resistance.

TimH
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Re: Output to AFR gauge - possible / any ideas on how

Post by TimH »

dr_jones wrote:Thanks Tim!!

That's a great help - the 'View - Customising Options' was the part of the jigsaw I was missing.
Don't worry - took me ages to find it too!!
dr_jones wrote:The gauges inputs are specced as 0v = 7.35 A/F and 5v = 22.39 - So I guess I'd need to use an IGN output to drive it (they seem to be the only 5v outputs) - however this brings with it a concern - there is a note there in the S6Plus pinouts and wiring guide about danger of damaging the ECU if the IGN outputs are directly connected to low resistance but nothing as far as I can see about what constitutes a low resistance.
Don't use the IGN outputs. Horribly useless except for ignition! (Well. might work, but are easy to blow up!). They can only deliver a couple of milliamps and we have no idea what the input of the gauge is - although you could set it up on the bench, with a 0-5V supply and measure the current it draws.

If it needs a 0-5V range, then you would use a PWM output with a pullup to +5V (use the sensor +5V). That way you'll have a 0-5V PWM signal. Probably 470R to start with. Ideal scenario would be to use an oscilloscope to look at the PWM volts - if the gauge draws too much current from +5V through the resistor you might not get the full gauge range.

Is it a stepper gauge? If so, I can imagine some "fighting" between the PWM and the stepper drive: play with the frequency until it seems to work. In the limit you could R-C filter the PWM to get a cleaner DC drive to the gauge, but don't worry about that until you've tried it with a direct connection.

pat
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Re: Output to AFR gauge - possible / any ideas on how

Post by pat »

Tim,

IGN outputs will be fine for this purpose. The warning is there for those people who like to connect non-transistor coils directly and then blow up the outputs. I've used IGN outputs numerous times to simulate a 0-5V analogue output. You can source and sink a couple of hundred milliamps which is fine for a gauge.

Some of the S6GPPlus FUEL outputs (erstwhile AUX outputs) are equipped with pullup resistors as part of the Plus carrier, two of which (11,12) can pull to 5V and two of which can pull to VBAT (9,10) so you could use these if you prefer of course :)

Cheers,

Pat.

TimH
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Re: Output to AFR gauge - possible / any ideas on how

Post by TimH »

Thanks Pat.

I once tried to drive a solid state relay from an IGN output. SSR needed >+3.5V to trigger, and 10mA, but the IGN output struggled to trigger the relay properly. I assumed it had no current ability being a "TTL" drive.

dr_jones
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Re: Output to AFR gauge - possible / any ideas on how

Post by dr_jones »

Thank chaps - this is a great help - I've not managed to test the theory as yet as I'm having ongoing wideband issues (separate thread) - the gauge I was intending to uses here is a digital gauge rather than a physical needle type (so no stepper motor etc) but from what I understand about digital volt meters this should work just fine.

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