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DIY: Remote Start Heated Seats

25954 Views 73 Replies 39 Participants Last post by  GXP25
Living through frigid Saskatchewan winters, I’ve always valued remote start on my vehicles. Even though our G8s have remote start, I’ve always found that I would hop into my semi-warm car only to find the leather seats are still ice cold. I figured I had to do something about this travesty, so here’s what I did.

The information contained hereon in is intended for entertainment purposes only. Any act or attempt to utilize the information, in part or in whole, will be at the reader’s own risk and the reader agrees to indemnify the author from and against any demands, claims, and damages to persons or property, and losses and liabilities, including reasonable attorney’s fees, arising out of or caused by the reader or their attendees’ interpretation of the stated information or negligence in assembly/installation of the portrayed device. It is strongly recommended that any electrical work be certified by a licensed Electrical Engineer.

Also, ignore the incredibly dirty car, I’m very aware it’s in need of a good cleaning.
The following parts/tools were needed for this project:
Plastic project box (I used 2”W x 3”L x 1”H, which was tight)
LM7805 voltage regulator
2N3904 transistor
100µF (min. 16V) electrolytic capacitor
0.1µF (min. 16V) electrolytic capacitor
PICAXE-08M, -08M2, or 08M2+ 8-pin microcontroller
8-Pin microchip socket
1.8kΩ ¼ watt resistor
2 - 1kΩ ¼ watt resistors
32kΩ ¼ watt resistor
5V N.O. DPST relay (or DPDT using the N.O. contacts)
2 - toggle switches
PCB Breadboard (or other type if you desire)
Screw terminals, totaling 5 termination points
20 gauge solid hookup wire (for component interconnections; stranded would work too)
16 or 18 gauge stranded hookup wire (for connection to vehicle wires)
Rubber grommet for wire exit from box
5 Red T-tap connectors (for connection to vehicle wires)
Soldering iron
Pliers to close the T-tap connectors
Digital multimeter for testing
2 - inline fuse holders with 1A fuses for the line from the front side of the factory switches and +12 line


**The 32kΩ ¼ watt resistor was recently added to the circuit as it is required for some variations of the PICAXE-08 microcontroller. Pin 2 is the programming pin and, in some final installations, needs to be pulled to ground so the chip knows it's not preparing for programming. If you do not do this, there is a very good chance that the chip will not function properly.**
The following is the circuit that is required for the controller box, along with the general logic of the heated seat control:

Theory behind the circuit:

The general principle of the circuit is to simulate a user pushing the heated seat button three times to turn the seat elements on high after a remote start. After analyzing the wiring diagram for stock control, I found that pushing the button simply provides continuity across two terminals/wires at the switch, which triggers a logic input at the vehicle’s heated seat controller. Therefore, pulsing a normally open relay would provide this continuity.

Also discovered by the stock wiring diagram is that both switches use the same 12V source that is used for signaling, shown as point “1” on the console switch block. Therefore, a single source point of voltage can be used and passed on through the relay contacts. This 12V point of supply is also the source of power for the entire circuit, which is dropped down to 5V through the LM7805 regulator.

As you can see from the schematic, I added two switches to manually defeat the module. The one switch is used as a manual defeat/enable for the entire unit, since opening this switch cuts off the primary power supply to the circuit. For me, this would mostly be used to defeat the unit during the summer months. The second switch is used to deactivate remote start heating of only the passenger seat if it would be a waste to heat it.

In terms of inputs, the module’s microcontroller only turns on if the 12V from the console switch is available and dropped to the usable 5V after the regulator to supply the chip power. This means that a vehicle start, either remote or manual, has been initiated. However, since I only want to turn the heated seats on with a remote start, I used another voltage reference, that being the accessory voltage. Since we do not have accessory power when remote starting, we can assume that heated seat control should only occur if accessory power is not available. The signal for 12V accessory (tapped off the back wires of the front console receptacle) is measured after a voltage divider, which provides proper logic voltages for the microcontroller input.

Assuming that the microcontroller turns on (aka vehicle start initiated) and there is a low input provided to the other input (aka indicates remote start), the microcontroller, after waiting 8 seconds for the vehicle to start and stabilize system voltage, pulses the output three times. This pulsing turns on the transistor, which allows enough current flow to energize the pull-in coil of the relay to close the contacts. Depending on how the manual defeat/enable switches are configured, either the driver’s heated seat button or possibly both seat control buttons will be provided continuity to simulate the user pushing the button(s). The diode shown in the circuit is used to stop backfeed of the magnetic field breakdown in the relay coil when it releases.
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Thanks for the excellent writeup,What if we only wanted low or medium seat heating? Is that possible through an additional switched logic circuit ?
Could some kind of temperature sensor be incorporated also with maybe a dashpot to allow an adjustable target turn on temperature so it would automatcally turn on at say 55 degrees and not on above that? negating the switch, And would you maybe be interested in selling just the programmed processor, relieving you from any liability issues?
If it was not for the chip programming,this would be so much easier
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