Smartphone Remote Control SH

Hello,

Let's do a small project .
You can use the controller to remotely control anything you want; it's an Atmel AVR Mega32 connected to a Siemens mobile phone (model S/C/M 25/35).
I know the M32 is a bit oversized, but I just happened to have some lying around, and they cost less than 5 cents each.

The whole process is very simple and can be done directly from a mobile phone to an AVR (microcontroller).
Call the mobile phone.
Save called number (button on the answering device).
With each subsequent call from this number, a relay will be activated. This relay is connected to a 'low-side' switch, regardless of what you want to use it for. The low-side switch is compatible with Webasto SH systems and also with the original Audi remote control.
After the phone rings and the number is recognized as valid, I let it ring three more times, then I hang up using the AVR (Automatic Voice Response) system to confirm that everything worked correctly, and this doesn't incur any charges.

The low-side trigger is currently set to 500ms, but I can adjust it if needed, making it longer or shorter.

When connecting power to the AVR microcontroller, a voltage of 5V is typically used with a regulator like a 7805 or similar.
/RST to 5V via a 10k resistor.
The AVR microcontroller runs with a 16 MHz crystal oscillator, but it can also be configured to operate at a different frequency.
Portb.0 is a button that connects to ground (GND) when pressed, used for saving the number.
Port B.3 is the output pin (low side or whatever).
Connect pin 14 (AVR / RXD) to pin 5 of the phone, and include a 1k resistor.
Connect pin 15 (AVR / TXD) to pin 6 of the mobile phone, and insert a 1k resistor.
Connect Pin 1 of the phone to ground (GND).
Connect pin 2 of the phone to ground (charge at 150mA).
Connect pin 3 of the phone to 5V. I'm using a 10 Ohm resistor for current limiting. A 7805 regulator gets hot when the battery is low (14V-5V + 200mA), resulting in 1.8W dissipation on the regulator!

An the PortD interface, an LCD screen can be connected to display the stored number and the number of the last caller, although this is not essential for its functionality.

Mobile phones and AVR (Automatic Voltage Regulators) should not be used in close proximity to each other, as the radio frequency radiation emitted by the mobile phone can sometimes disrupt the operation of the AVR. Problems typically disappear when the distance between the two devices is increased to approximately 30 cm.

The images and the hex file are attached.
(This is an AVR board that I built, and it's not just for the phone; the voltage regulator on the board isn't available on the open market, but it's used in almost all ECUs . A 7805 would work just as well, but the one I use also has a watchdog (which is not needed here) and a reset generator.)

I've now attached the schematic for the AVR board, including a 7805 voltage regulator. For this phone project, only the microcontroller (uC), voltage regulator, and low-side driver are needed; the rest of the components are not necessary.

Feel free to contact me with any questions.

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1. Does the phone actually charge with 5V? My S45 only charges between 6.1 and 8V. Does the phone reliably charge at temperatures as low as -15°C?

2. The phone's RS232 interface does not use TTL logic but operates with a 3V logic level. In fact, the high level on the TX pin is 2.8V. Will the AVR correctly recognize this signal?

3. What do you call a "low-side" connection? Have you connected your circuit to the instant heat button on the timer?

'Yes, the phone is charging, but it's just a trickle charge to maintain it. The battery only has 3.4 or 3.6V, I'm not exactly sure. With some batteries, this can actually cause problems when it gets really cold. Usually, I remove the battery and power the phone directly with an LM317 regulator, which eliminates any issues and prevents the battery from being damaged.'
2. The phone doesn't operate at 3V; it uses 3.3V. The high level signal isn't the problem; it's correctly recognized that the AVR is outputting 5V, which is more of an issue. The microcontroller in the phone operates at 3.3V, resulting in a 1.7V difference. Subtracting the 0.6V drop across the ESD diode leaves 1.1V. With a 1k resistor, this translates to approximately 1.1mA, which is then acceptable.
3. In a car's ECU, low-side or high-side drivers are built-in amplifiers, usually low-side ones where the load is connected to V_batt and the switch connects to ground, typically using a simple transistor or FET (in the ECU, these are often multi-stage amplifiers).
I'm using a FET, for example a BSS138, which has a logic level input. The microcontroller (MCU) usually has an internal pull-up resistor, and the button only connects to ground, which is then also what the low-side switch does.
This setup has been assembled approximately 15 times and works with both the original Audi control unit and the Webasto controller.

If there are any further questions.

Hello,

'Due to some inquiries regarding the A4, a radio receiver (R64) has been installed. It is connected via a cable to the SH control unit at J364. Does anyone know what kind of signals are present there? Specifically, I'm interested in whether they are used for turning something on or off – are they pulse signals or static states? Or perhaps it's even a data line?'
The connection should be made via T10k/1, with a plug located on the left A-pillar. Where is the plug? Then I could measure the signals myself.
Then it would be possible to turn on the SH even without radio communication, simply by tapping into the cable.

THX

Hi Nicklas,

Can you please attach the block diagram as a lossless image?

I also want to experiment with AVR microcontrollers and I'm currently reading up on them, but unfortunately, very little is visible in the JPG image "AVR_s25.jpg".

Thank you.
Martin.

Is that the AVR board a custom-designed one or a commercially available product?

If purchased, which one? Where can I buy it? How much does it cost? Is it any good, or does it have any weaknesses?

Thank you.
Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Hello,


The board is self-built and therefore has no weaknesses .
No, it's designed according to my preferences; everyone probably feels something different about it.
I would add a few more standard connectors for an oscilloscope or whatever else might be needed; I always seem to be missing the right connector. Otherwise, I have no complaints.

Hello,

I have replicated the SH remote control. It works perfectly. I would like to clock the ATmega32 with the lowest possible frequency instead of 16MHz.
(lower power consumption). Can anyone help me with this?

Thank you.