Delayed button press

[psaffrey]

I bought a dishwasher with no delay feature. A delay would be useful to take advantage of off-peak cheap electricity, so I thought I would try to make something do the job as a "fun project". Rather than risk damaging the dishwasher itself, I was hoping to make a device that just presses the button on the front - the small-travel clicky sort, rather than the big on/off button - at some specified time.

My plan is to buy an alarm clock, take it to pieces and make it so that when the alarm is due to go off, instead it activates a physical switch. Then I attach the device to the front of the dishwasher with suckers or similar. Set the alarm time and turn it on and at the chosen time, it moves the switch.

There are a few sticking points, mostly based around the problem that I've never really done this kind of hardware stuff before - I'm a software engineer. I could do this with Lego Mindstorms, but that seems like overkill. I thought it might be fun to learn something new

• What kind of device do I need to do the switching? An actuator? A solenoid? Can I get one of these fairly cheaply (I'm thinking less than £10)?
• The kind of alarm clock I have in mind is driven by a single AA battery. Would this be powerful enough to drive something hard enough to press a clicky button?
• The button has to be pressed and released to set it going - otherwise it will just reset. I'm not sure whether to do this on/off behavior with the clock or the switching thing. Any suggestions?

This sounds like the sort of project somebody might have tackled before, but some naive googling didn't reveal anything. Does anybody know where I might go to find some good web resources on this kind of project?

Peter

[Thomas W]

Hi Peter,

Maybe you could use some kind of micro server motor to do the physical switching: http://www.robotshop.com/ca/hitec-hs55-servo-motor.html
A state machine built from flip flop IC's or a counter IC would probably be needed to reverse the direction of the motor, once the button has been pushed in.
Whether you'll have enough power in an AA battery depends on the actual motor you choose. The datasheet will state the power needed.

What alarm clock model did you choose?

[psaffrey]

Thomas,

Many thanks for your reply.

For the alarm clock, I had something like this in mind:

http://www.ebay.co.uk/itm/New-Casio-Com ... 20b1ef274b

It has a very simple interface - you turn the alarm hand to a particular time and flip up the button. When it reaches the right time you can hear it click as it activates the alarm. I'm hoping this simplicity will make it amenable to this kind of surgery!

The IC/servo solution seems sensible. Is there some introductory material you might recommend on designing and building such a circuit? I guess I buy a small breadboard, a soldering iron and a few small off-the-shelf chips?

Peter

[Thomas W]

I found this type of solenoid that you could use as actuator instead of a servo motor:
http://uk.rs-online.com/web/p/d-frame-solenoid/2501303/
I was worried that a solenoid would smash the button but I think it would be a matter of placing the pin directly on the button with no air gap, so that the pin is in contact with the button at all times, and let the spring in the button push it back when the power is removed from the solenoid.
You would have to find just the right solenoid so that it won't smash the button due to too much power being used. The above one pushes with 400 gram, but I'm not even sure it's enough. It would take some experimenting to get it right. Unfortunately it uses much more power than a small motor.
The ON/OFF control could be handled by a 555 timer IC:
http://worldnewsfrommyiphone.blogspot.c ... rcuit.html
One trigger pulse from the alarm clock resulting in a controlled trigger pulse from the 555.
(And please post pictures of the dismantled alarm clock... )