Mechanical Timer with Specific Components

[JWM1270]

Hi. I am new to the forum so forgive me if I don't say something correctly or if I'm in the wrong section.

I am working on a project. I want to produce a device that has a built in timer. I want the timer to have 2 modes. Manual mode and 'Device' mode. The manual mode is just like it sounds, you could turn it on and it would stay on until you turn it off. In the device mode each time the user would manually set the time remaining, probably in 30 minute intervals up to 4 hours, in which during this time the device would remain OFF and after that time had elapsed the device would turn ON for 15 seconds and then turn OFF and stay that way until the user decided to use the device again. I'd also like to have a clock included so that the user could set a time in which the device would turn ON (again for a set, built in time of 15 seconds) and then turn off until the same time the following day if the user continued to have it on this setting. I guess that might be 3 modes. It may sound strange but I have my reasons.

Does anyone have any suggestions? I'm not an electrical guy (my degree was Civil Engineering) but I'd like to put this together or hire someone to design it for me. Mechanical timers that exist in the marketplace have these features but not the part where it automatically shuts off after 15 seconds. Any assistance is appreciated.

Thank you,

John

 

[BradtheRad]

Someone will no doubt suggest a microcontroller for your project, as the simplest method.

If you don't go that route then you'll need to construct several circuits, including a 24-hour clock which is user-settable via push buttons, and provides a trigger-out signal.

In addition you'll need a 4-digit display, and a 15-second timer circuit which drives either a relay or transistor.

To handle the user-chosen time of 30-minutes to 4 hrs, will require (a) another timer circuit, and (b) a way to make this setting override the 24-hour clock.

For the 24-hour clock section, you may get by with a counter driven by an accurate frequency base (such as a crystal). Suppose you have 4 digits, and you set an increment of 10 seconds. It would (a) load 8640 as binary, (b) count down to 0, (c) send an enable pulse to your device, then (d) repeat.

 

[JWM1270]

Cool. Thank you for the info!