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Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
a'm working on a project to design a phone operated safe, i need help on how to interface the DTMF DECODER with cellphone, circuit and also how the tone would be detected on the microcontroller chip
you might want to take a look at that design. If the mainboard is housed in the safe the code can only be changed while the safe is open.
There are just two parts outside the safe which are the electret microphone an LED signaling valid code.
The device uses four digits and receives the DTMF decoded signals from a CM8870 (Q1-Q4). The single digits are then being compared with the values put in by switches S1-S4.
Till now no software has been written and no board has been built.
The design is meant to give you an idea how achieve your goal.
Thats a complex circuit, I've done just this with a pic a decoder and a dual opamp chip (romans done it without the decoder which is quite clever), I think I could do away with the op amp and use a tranny, mine is for acces to a building.
My circuit doesnt have a phone line interface, re-reading your op you dont either, you just want a mic, if you want I'll see if I can find my schematic, its very sensitive so you can turn the volume down on the fone to protect against it being recorded.
I dont think the firmware would be of much use to you I never bothered with being able to change the code, its burnt into the chips program memory, for a commercial product you'd want it user programmable and stored in the pics eeprom.
Heres an interesting article, I used both op amps in the lf358 this guy doesnt:
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