Jscoyne2
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Joined: Mon Nov 18, 2019 1:28 pm

What would it take? Vehicle HVAC controls

Mon Nov 18, 2019 1:41 pm

Hey all. I don't know anything about Pi's or programming for that matter but i have a question about the viability of an idea.

I am a big mobile audio enthusiast and im looking into integrating a tablet as both my stereo headunit and hvac control unit. Doing the stereo part is easy and im a pro at that but the hvac is a lot trickier. Many cars have something like a 44pin connector that plugs directly into the hvac control unit and its the entire brain.

I'd assume the HVAC controls would just be like anything else in the car. Either 12volt on or off, or a variable voltage sensor.

Ie:
3 volts cold air
3.4 volts warm air
3.7 volts. Hot air

It would take some testing to verify that but if thats the case. How difficult would it be to have an app on the tablet control the Hvac?

It may be possible to send a specific voltage out of a tablet through some kind of OTG cable but i was thinking more on the grounds of having an app connect via Bluetooth to a hidden Pi and have the PI do send out the correct voltages to the correct wires.

I know im asking a lot here. I'd have to learn to code both for an app as well as a PI. Plus figure out the wiring but i thought I'd ask if anyone sees any large red flags.

Thanks for your time.

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topguy
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Re: What would it take?

Mon Nov 18, 2019 2:28 pm

I'd assume the HVAC controls would just be like anything else in the car. Either 12volt on or off, or a variable voltage sensor.
I know nothing about cars or their HVAC but this sounds like a rather big assumption.

The Pi don't have Analog controllable outputs, only digital 3.3V inputs/outputs so you would need more electronics regardless.

pfletch101
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Re: What would it take? Vehicle HVAC controls

Mon Nov 18, 2019 4:03 pm

Jscoyne2 wrote:
Mon Nov 18, 2019 1:41 pm
I'd assume the HVAC controls would just be like anything else in the car. Either 12volt on or off, or a variable voltage sensor.
I agree with topguy. Without knowing how the HVAC system controls work, you are likely to have major problems interfacing with them in a way that won't damage or destroy either your control system or the car's HVAC system, or both. There are always many ways of getting things wrong in a complex electrical/electronic system, and far fewer of getting things right. I have no knowledge of car systems at the necessary level, and I suspect that the information you need is either regarded as proprietary by the car manufacturers or, at least, not easily available to the lay person. You may find more help on a car enthusiast or technician BBS.

K0ENIE
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Joined: Thu Apr 02, 2020 7:38 am

Re: What would it take? Vehicle HVAC controls

Thu Apr 02, 2020 8:43 am

I think it's possible, depends on what system the car's using. I build HVAC from a saab 9000 into a 1972 DAF variomatic so I know what hardware this uses. We have 2 analogue temperature-sensors, a 'sun'sensor (!) 3 steppermotors (bipolair) to control airflaps and hot air flap, binair operated resistor unit for the blowerfan, and some I-O outputs for the airco and coolingfans and so on. Steppermotordriverboards are available for the raspberry.

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thagrol
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Re: What would it take? Vehicle HVAC controls

Thu Apr 02, 2020 12:36 pm

Jscoyne2 wrote:
Mon Nov 18, 2019 1:41 pm
Hey all. I don't know anything about Pi's or programming for that matter but i have a question about the viability of an idea.

I am a big mobile audio enthusiast and im looking into integrating a tablet as both my stereo headunit and hvac control unit. Doing the stereo part is easy and im a pro at that but the hvac is a lot trickier. Many cars have something like a 44pin connector that plugs directly into the hvac control unit and its the entire brain.

I'd assume the HVAC controls would just be like anything else in the car. Either 12volt on or off, or a variable voltage sensor.
That's a big assumption and not one I'd make on any reasonably modern car. It's equally possible that communication between the dashboard controls and the HVAC is via messages on the car's CAN bus. The days of complex point to point wiring harneses in cars are long gone.

Find the repair manual for the car and the HVAC system. Don't start poking around in there based on assumptions. If you damage the HVAC it's likely to be an expensive repair.
Arguing with strangers on the internet since 1993.

PhatFil
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Location: Oxford UK

Re: What would it take? Vehicle HVAC controls

Thu Apr 02, 2020 12:50 pm

If your assumptions are correct?

you can use a voltage divider (2 x resistors) to drop a voltage from one level to another..
https://learn.sparkfun.com/tutorials/vo ... viders/all

you can use a mosfet to switch dc voltages on/off via a Pi gpio pin
http://www.robertcudmore.org/blog/?p=181

For your gui you could consider employing the Node Red dasboard, host node red on your pi and use flows to control the above circuitry, and use the dasboard to provide your i/o accesable via a browser.

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topguy
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Re: What would it take? Vehicle HVAC controls

Thu Apr 02, 2020 4:35 pm

FYI: This thread is 4 months and the last time the TS was online was 6 hours after his first and only post..

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thagrol
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Re: What would it take? Vehicle HVAC controls

Thu Apr 02, 2020 5:20 pm

topguy wrote:
Thu Apr 02, 2020 4:35 pm
FYI: This thread is 4 months and the last time the TS was online was 6 hours after his first and only post..
Oops. Usually check the date the thread was opened before responding. Forgot this time, obviously.
Arguing with strangers on the internet since 1993.

PhatFil
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Location: Oxford UK

Re: What would it take? Vehicle HVAC controls

Thu Apr 02, 2020 6:18 pm

Ha.. Facepalm.. DOH!

well spotted.. :lol: ;)

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