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Hi, i am designing a Electronic Lock at the moment using a keypad. Now all is ok apart from when i try and wake up the lock from sleep mode. I have to use a low level trigger but the problem is when i press a button the voltage is only being pulled down to 1.7V. To pull the interupt down i am using a PORT on the AVR, please see the attachment for circuit.

Can anyone help me to solve the problem

thanks

James

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Hello James,

I'm not sure I fully understand the problem or what you're trying to do in your schematic. But one thing that you can do to solve these logic level problems is to buffer logic lines with a transistor. Just configure the circuit to be an emitter follower or an inverter.

Could you maybe describe how your project is supposed to work? Something like, "when this goes high and a button is pressed, I expect to see ___ on this pin... "

Regards,
Paul

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Paul,

I have managed to solve the problem now, as always it was a human error. The circuit is used to scan a 4 by 4 matrix, when a button is pressed it will pull down the ouput port to gound. Now i was in sleep mode on the AVR and had set the pull up resistors, but in onwe of my delay routines i had turned them off. This meant the circuit could not work, it solved now though.

Thanks for your time

James

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Hi

Isn't this from the Atmel application note.
AVR240: 4x4 Keypad-Wake Up on Keypress
The AT90S1200 chip is obsolete.
Did you happen to have one lying around ?

So you will need to add more code to turn this into a Electronic Lock?

Ken

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Ken,

The keypad is from the ATMEL application i am running it on a ATMEGA88 All code is done now. It uses Master and slave operations and should have a good battery life on 2 AA batteries. Next is to design the i-button version, i should be able to use the same setup i just need to come up with the comms protocol for the 1 wire apps.

thanks

James

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Hi James

Glad thing are going well for you.
It sound like you have a reasonable background of electronics & programming.
Pretty good for a newbie.

Just curious what compiler are you coding in(C, Asm) for your project?

Cheers
Ken :)

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Ken,

I'm new too AVR's and design really i have been working in Automotive electronics as a test engineer for the last 3 years. Before that i was at uni doing Electronics and computer sciences working with PIC's in C.

As for this project i am using C, simply polling the buttons when out of sleep mode, then i am comparing the results to a known value to see if it can open. This is all ok for the Keypad im just worried about the 1 wire i-button project. Also my manager wants me to look into voice and finger print locks, which means moving upto ARM processors which i have never worked on.

What do you do, are AVR's work or hobby.

James

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James,

Quote:
What do you do, are AVR's work or hobby.

I do both & program in Asm.
Quote:
voice and finger print locks

A tall order for this request.

Ken