Welcome to the workshop. Before I tell how to rework an ordinary cellular phone - here an Alcatel One Touch Max db was used - into a remote, shortly the disclaimer that the modification is on your own risk and the guarantee will definately be gone.
The following rework has been done by myself and was rather easy and cheap.
The aim was to get a remote for my car's stand heater Webasto Thermo Top T as the original one from Webasto was with € 500,- a little bit too expensive to me. What was more obvious than reworking a cheap prepaid cellular phone to do that job? (Well giving up was not an option!).
Tools & Material
- Generic cellular phone
- Solder iron and solder
- Relais with small coil voltage
- Transistor NPN-Darlington BDX 33A
The cellular phone ist opened and one led of the
keyboard illumination is removed. Then a twin core cable is soldered to the two
led contacts and lead outside of the phone. Now the following construction is
build into a separate case.
My car stand heater features a control unit with a key to manually switch on the heater for 30 minutes. Now when the cellular phone is called the keybord light is switched on and activates the relais via the transistor which then activates the heater or any other unit. Thus I have soldered the switching pins of the relais parallel to the above mentioned key.
It is very important that the cellular phone does not activate the keyboard light on its own e.g. when losing the network signal or the battery is low. Connecting the phone to an external antenna makes sense especially when using a switch with an already installed car kit. The Alcatel One Touch Max db is very good in this aspect as Alcatel phones feature a very good reception and I got it for only € 30,-.
An alternative solution is CosyCall.
Meanwhile WEBASTO offers a similar ready to use product Thermo Call TC1 which is available for about € 500,-. Buy this unit if you need a reliable solution and have the money.