Remote Control of the Central Heating using a Mobile Phone

22 January 2008

Arriving back from a few days away to a cold house in the evening is not nice. I could leave the heating on, but this is becoming increasingly expensive.  What if I could phone home and have a computer fire up the boiler?

1. Mobile dials home number.
2. Modem outputs to microprocessor the character sequence: RING
3. Microprocessor sends ATZ and waits for OK
4. Microprocessor sends ATH1 to modem to put it on line.  

– Numbers from mobile keypad are now transmitted to the modem as audio DTMF coded tones
– These tones can be heard on the modem’s loud speaker
– A DTMF decoder chip can translate these tones back into digits
– The digits are fed to the microprocessor, and represent instructions

5. Microprocessor requests password (by using a speech generator to say “Password” down the audio link)
6. The 4 character password is entered using the mobile’s keypad
7. If the password is false, microprocessor causes modem to hang up by sending ATH
8. If the password is OK, microprocessor says “Welcome”
9.  Pre-decided number codes can now  fire up  the central heating etc.
10. When done press 9
11. If microcomputer receives digit 9 it sends the modem ATH to cause it to disconnect, or hang up

Initially the modem and microprocessor are assumed to be on and connected all the time,
 however, it should be possible to only have them on after the phone has rung, thereby saving electricity.

Also there is no reason why the microprocessor cannot dial the mobile, and this will give a whole new meaning to the doorphone!  
e.g.  If the Fed-ex man rings the door bell with a parcel, the microprocessor patches the doorphone through to your mbile, and you can talk to him from anywhere on the planet, and ask him to leave it next door.  O.K.

The modem is a ten year old TI 5600 but it still works. The following codes have been tested and they work: ATZ,  ATH1,  ATH.  These are needed for the initial project. ATDT<mobile-number> also works, initiating an audio channel between the microprocessor and the mobile.

It is taken for granted that the project will use a HD6303XP, – cos I have quite a few of them left over from the company, and there seems to be a steep learning curve associated with PIC technology! 

Because my Archimedes 5000 is now on it’s last legs, I was pleased to find a MC6800 assembler that runs under XP and Linux called masm. This is now installed on the Linux box called Penguin, and works a treat.  An early job will be to port Alex’s Famous Monitor assembler code to masm format, and write additional bits to upload code from  Penguin to the 6303s RAM for testing.

Also the EPROM blower needs to be tested. – haven’t used it for ten years or so.  -and what happened to the EPROM eraser?

I have a DTMF decoder chip, and a few circuit diagrams of how other people have used it.  This will need breadboarding and testing.
JOBS:
1. port monitor to masm
2. find EPROM eraser
3. test EPROM blower
4. get a simple monitor running on one of the old PCBs with serial o/p to minicom, (the Linux terminal program)
5. breadboard the DTMF chip

Halfway through testing, I’d got the DTMF stuff working, and resurrected the ability to create machine code with masm and blow it into EPROM and run it, the Raspberry Pi came to market. As the Pi could access the internet, and serve interactive web pages, whereas the 6303 could not, it seemed to be a far better option than mucking about with DTMF codes!So the Mark I version was abandoned, and all efforts became focussed on learning how to use the Pi. 

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