What is the MODULE SEAT HEATER and how does it work

[Ste Cooper]

Hi all

 

Looking through the wiring diagrams available on this site for the MK2.5 focus, around the heated seats.

I think I get the concept of how they work, the pads act like a resistor so they heat up when current passed through them.

I assume then to vary the temperature you limit the current that can flow through them.

That said I'm trying to understand the following wiring diagram and specifically the component named MODULE SEAT HEATER and how it works in relation to the above assumption.

(its one page 97 BTW)

I suspect the switch it self does not directly feed the elements otherwise it would have to be quite beefy to not burn out, so i assume there is some form of relay inside the MODULE SEAT HEATER. It also has its own direct power feed to that makes sense if there is a relay in there.

However looking at the diagram the switch appears to contain a 5k potentiometer (if iv'e read it right) which explains the fact its a scroll wheel, however now I'm confused. If it is a simple relay in there how does the variable resistance of the dash switch change the resulting heat? Because that switch would trigger the relay?

I assume there is something other than a relay doing it, but my knowledge of electrical components here really lets me down.

Tried searching on eBay for one of these module and not found out. I was hoping to open it up and see what exactly is inside.

 

Any help in understanding how this system works would be great thanks.

[JW1982]

The switches are basically just potentiometers (variable resistors) that output a resistance signal. Based on the resistance the heated seat module determines the position of the switch. This information is used to control the seat heating pads. 

The modules contain an advanced circuitry that acts as a thermostat. The module uses PWM to control the heating pads. According to the position of the switch the module outputs a duty cycle. The frequency of this signal regulates the temperature of the heating pads.

[Ste Cooper]

Fantastic thanks, exactly the info i wanted! 

It should be quite simple to use an Arduino or similar to achieve the same behavior. Being a software developer by trade that side of things is easy, its the hardware side i struggle with.

[mjt]

You don't need anything as complex as an Arduino for something like that. A PICaxe would be quite adequate.

[Ste Cooper]

On 7/7/2020 at 10:55 AM, mjt said:

You don't need anything as complex as an Arduino for something like that. A PICaxe would be quite adequate.

Not heard of them ill have a look.

Always used Arduino's because im familiar with them. And got the equipment/IDE already available/configured (setting up VSCode for that was a huge PITA).

I would use the Arduino whilst developing, then use the MCU directly with my own PCB in production.
Its what im doing with the powerfold mirrors, got a stack of relay and canbus shields but when finished ill be able to fit all on one small PCB (or at least thats the plan)
 

[StephenFord]

I read this thread out of curiosity - my head hurts... 🤣

[TomsFocus]

Wouldn't it be easier just to buy the module?  Heated seats weren't all that rare in Mk2.5s so there must be plenty in scrap yards now?  

[ScaniaPBman]

For me it would be much easier, I haven't a clue what they are talking about!

ScaniaPBman.

[JW1982]

The Focus MK3 (and several other Ford models) uses the exact same module and are easy to find. 


However developing and building a more advanced module yourself is a lot more fun. Arduino is a very nice and cheap solution for development and testing. I am currently developing a CANbus module that converts the position of the heated seat switch to a CANbus signal that communicates with my aftermarket Android radio. Based on this signal the radio displays the heated seat signal.

[mjt]

On 7/10/2020 at 11:11 AM, Ste Cooper said:

Not heard of them i'll have a look

It's an educational version of the 8-bit Microchip PIC microprocessor. It has a built-in loader so all that's needed fror programming is a special USB cable with a standard 3.5mm jack plug. That means it can be programmed in-circuit. The development software is free. It uses a form of compiled BASIC so pretty simple to learn. There's a family of chips with varying degrees of functionality but I'm sure it could do what you want quite easily in a 16-pin DIL package. See here.

I've also used Arduino for a more demanding project and chose it because I was already familiar with the C language. Just made my own shield board to piggy-back on it.

[Alex.S]

Knew I should’ve stuck in at school...🤔😞

[Ste Cooper]

11 hours ago, TomsFocus said:

Wouldn't it be easier just to buy the module?  Heated seats weren't all that rare in Mk2.5s so there must be plenty in scrap yards now?  

It would, but i enjoy building things and figuring out how stuff works, cant do that if i just buy it 🙂
 

10 hours ago, mjt said:

It's an educational version of the 8-bit Microchip PIC microprocessor. It has a built-in loader so all that's needed fror programming is a special USB cable with a standard 3.5mm jack plug. That means it can be programmed in-circuit. The development software is free. It uses a form of compiled BASIC so pretty simple to learn. There's a family of chips with varying degrees of functionality but I'm sure it could do what you want quite easily in a 16-bit DIL package. See here.

I've also used Arduino for a more demanding project and chose it because I was already familiar with the C language. Just made my own shield board to piggy-back on it.

Awesome ill look into it. Yea im in the process of learning C. Mostly used to more abstracted languages like JS and C#. Not having dynamically allocated arrays was a big culture shock.

Had a similar idea using an arduino, and an app on a rooted tablet to get IO via the tablet. Wasn't too sure on the coms between the arduino and the tablet, maybe some form of serial. Got the arduino reading CAN data from the car, struggling to properly understand the purpose of most of the messages though. However i have dozens of projects on the go and never seem to finish one before the next pops into my head! So the tablet idea hasn't evolved on from that yet.

Do you have any of your source on Github/Bitbucket etc? I'd be really interested to have a look through.

[mjt]

9 hours ago, Ste Cooper said:

Do you have any of your source on Github/Bitbucket etc? I'd be really interested to have a look through.

'Fraid not. I suspect I'm not in your league so my code would probably not be especially interesting anyway

[Ste Cooper]

On 7/11/2020 at 10:05 AM, mjt said:

'Fraid not. I suspect I'm not in your league so my code would probably not be especially interesting anyway

Nah doubt it.

At work we call it pair programming. Iv'e found that regardless of any perceived experience gap its still beneficial from a learning point of view for all involved. I enjoy looking at others code, always learn something new.

Anyway thanks for all the info, ill look into it 👍