Car AC Control

After completing an android tablet install into my car, I set out to control the AC knobs with the tablet. Arduino seemed to be the best solution to accomplish this. While I've been programming for years, the hardware side of Arduino is somewhat new to me. I'm planning on using the Arduino Uno for the board, and wiring 3 servos up via a breadboard to turn the knobs via timing belts with pulleys attached to both the servo and the knob. The servos have to be powerful enough to turn the knobs. I'll also need a Bluetooth module to connect to the tablet, it will only be transmitting a few inches, so strength isn't a large concern. I've also set up a power inverter in the car to power everything, so I will need some type of power cable.

What I have so far- Board: https://www.sparkfun.com/products/11021 Bluetooth Module: https://www.virtuabotix.com/?p=373 Servos: Don't know on this one, not sure how much torque they need Breadboard: https://www.sparkfun.com/products/9567 Timing pulley/belt: not sure yet on this one either Power cable: Still need to pick one here too.

I'm trying to keep this build as cheap as possible with it still being effective. If you have recommendations or guidance as far as what to get, I would really appreciate it.

I don’t see any need for an inverter, and so far the reason for the breadboard is not obvious either. The Arduino can control a servo, so it seems to me that the area of biggest uncertainty is designing the mechanism used to drive the AC controls, and speccing the servo capable of operating that mechanism.

Might it make more sense to replace the car's AC control board with something that your arduino can control electrically? Using a multimeter, you should be able to figure out how the knobs control the HVAC and replicate that functionality with your arduino.

Also, while it's certainly possible to use the things you've picked out for this purpose, have you had a look at the IOIO board? It's designed to do exactly what you want, and it can use a tiny USB bluetooth dongle (be sure to check the compatibility list!) to talk to your tablet.

As for power, I don't know how you plan to mount/use the tablet exactly, but your car almost certainly has 12vdc available all over the place. That 12v can power your tablet, your arduino, your IOIO... all much more efficiently without an inverter.

PeterH: I don't see any need for an inverter, and so far the reason for the breadboard is not obvious either. The Arduino can control a servo, so it seems to me that the area of biggest uncertainty is designing the mechanism used to drive the AC controls, and speccing the servo capable of operating that mechanism.

Let me clarify a little. I'm using 3 servos(one for each ac knob) hence my belief that I need a bread board to hook all 3 up. http://1.bp.blogspot.com/-Syp68xkMghw/UIGk1lhCiQI/AAAAAAAAAC8/Ccep16ieiEE/s1600/3servos+bread_bb.jpg

The inverter is already in the car as a part of another project, so I figured it would be a convenient way to power this setup. I have an idea of how I want the mechanism to work: attach timing pulley to both a.c.knob and servo head and run a timing belt in between to turn the knob when the servo turns. However as you said,I do need assistance speccing the servo and choosing the proper timing pulleys.

djjoshuad: Might it make more sense to replace the car's AC control board with something that your arduino can control electrically? Using a multimeter, you should be able to figure out how the knobs control the HVAC and replicate that functionality with your arduino.

Also, while it's certainly possible to use the things you've picked out for this purpose, have you had a look at the IOIO board? It's designed to do exactly what you want, and it can use a tiny USB bluetooth dongle (be sure to check the compatibility list!) to talk to your tablet.

As for power, I don't know how you plan to mount/use the tablet exactly, but your car almost certainly has 12vdc available all over the place. That 12v can power your tablet, your arduino, your IOIO... all much more efficiently without an inverter.

I unfortunately can't replace the ac controls because the hvac uses vacuum tubes in place of wires for the main knob. I haven't looked at the ioio board, but I'll check it out. My car 12vdc are constant on, and I wanted ignition based power, additionally the tablet I installed in the dashboard wouldn't charge properly off of 12v, but it charges fine with the inverter. It wasn't ideal, but it works

That must be an old car... mind if I ask what it is? you should still be able to replace that with a more modern circuit that can be directly interfaced with your arduino.

FWIW, if you're charging off of an inverter, you are charging from the 12v. You're just doing a lot of unnecessary conversion in the process. 12VDC->110VAC->5VDC. If you need the 110 for another project it makes even more sense to power the tablet straight from DC, thus saving the available capacity of the inverter.

You don't need a breadboard to connect 3 servos to your project. Breadboards are generally just used to prototype circuits before transferring them to something more permanent.

You don't need a breadboard to hook single or multiple servos up. All you need is to connect each servo's ground to the common ground, +ve supply to the power supply you will provide for the servos (supply also grounded to the common ground) and the signal line to the appropriate output pin on the Arduino (which is also grounded to the common ground).

When converting from unregulated 12V DC to unregulated 7V DC, doing it by generating high voltage AC and then passing that through a transformer / rectifier is not the most obvious solution. Give yourself an easy life and get some DC voltage regulators.

PeterH: You don't need a breadboard to hook single or multiple servos up. All you need is to connect each servo's ground to the common ground, +ve supply to the power supply you will provide for the servos (supply also grounded to the common ground) and the signal line to the appropriate output pin on the Arduino (which is also grounded to the common ground).

When converting from unregulated 12V DC to unregulated 7V DC, doing it by generating high voltage AC and then passing that through a transformer / rectifier is not the most obvious solution. Give yourself an easy life and get some DC voltage regulators.

Okay, nevermind about the bread board then, showing my inexperience I suppose.

djjoshuad: That must be an old car... mind if I ask what it is? you should still be able to replace that with a more modern circuit that can be directly interfaced with your arduino.

FWIW, if you're charging off of an inverter, you are charging from the 12v. You're just doing a lot of unnecessary conversion in the process. 12VDC->110VAC->5VDC. If you need the 110 for another project it makes even more sense to power the tablet straight from DC, thus saving the available capacity of the inverter.

You don't need a breadboard to connect 3 servos to your project. Breadboards are generally just used to prototype circuits before transferring them to something more permanent.

It's not that old, it's a 2000 firebird. If you know of something that would be a better solution, I'd be interested in taking a look.

"I set out to control the AC knobs with the tablet. Arduino seemed to be the best solution to accomplish this."

Servos. Timing belts ... got fingers ?

after a bit of googling, I see that it uses vacuum /lines/, not /tubes/. Seems like a silly distinction, but vacuum tubes are something specific in the world of electronics :)

I'm not sure right now how I'd interface with that system but I'm pretty sure it can be done in a better way than operating the knobs with servos. I'd start by figuring out what the panel does with that vacuum.

djjoshuad: after a bit of googling, I see that it uses vacuum /lines/, not /tubes/.

I'm failing to follow how that works. Is it using air tubes as a crude hydraulic system, or something? Perhaps it's using the switch to connect an actuator/sensor to a vacuum source somehow, although this isn't a scheme I'm familiar with. Could it be connecting it to manifold depression, so that the AC automatically drops out when you open the throttle? That could be a neat trick.

I guess you need to decide whether you want the Arduino to move the physical controls (so you can see what it's doing) or work behind the scenes to override the manual controls. If it's moving the physical control you also need to decide whether you still want them to be available for manual use, and if so how the manual/automatic controls will work together.

from what I can tell it is using vacuum to control the vent damper/plenum. The switch in the dash acts as some sort of proportional valve, altering the pressure (I know pressure isn't the right word for vacuum measurement, but the correct term escapes me) to control how the damper/plenum is positioned. It's funny you mention the AC dropout at WOT. That's not the reason they did it, but it is a problem for firebirds and camaros. The vents (just the airflow, not the actual AC) shut off temporarily under heavy engine load when a particular part has failed. There is a little nipple covering a port on a check valve under the hood. That comes off or degrades, and you get the airflow issue. FWIW, AC already has a drop-out mechanism on most modern cars, it just works to shut off the compressor instead of the airflow :)

A large part of the reasoning behind automating the ac controls is that they are covered, and sit behind, the tablet installation. Sorry about getting the word mixed up, it was early and I was typing from memory. Either interfacing method will work for me, I'm just not sure how to go about it. The manual controls don't need to be usable,I won't be able to access them.

In that case the most promising approach I can see would be to install valves in the vacuum lines that you can control via the Arduino. This could be a solenoid valve that you can control via PWM, or one of the many idle control valves, or a simple tap operated by a servo. I expect that operating the valve directly would involve far less mechanical issues than trying to operate the hand controls.