0
\$\begingroup\$

I need to create a timer system with the following characteristics:

The system receives a post-key input signal (12v) from the ignition of a car. When this input signal is recognized the system activates an output and sends (12v). If the post-key input signal (12v) is switched off (0v) the output remains on at (12v) for 10 minutes. If after 10 minutes the input remains off (0v) the system deactivates the output (sends 0v to output). Each time the input is activated (12v) and then deactivated (0v) the system should start counting up to 10 minutes and then turn off the output. If during the countdown the input is activated again the count must stop and wait until the input is deactivated and then start counting again.

I must do this without the use of microcontroller. I have to use integrated circuit timer, does anyone know of any circuit that can help me do that?

\$\endgroup\$
8
  • 1
    \$\begingroup\$ 555 in monostable config will do. \$\endgroup\$ Commented Nov 3, 2017 at 11:34
  • \$\begingroup\$ Why must you do it without a microcontroller? That's would most of us would use nowadays. \$\endgroup\$
    – Finbarr
    Commented Nov 3, 2017 at 12:01
  • \$\begingroup\$ I am limited in design time and cost. And the number of boards that are produced does not make up for the cost of a project using microcontroller \$\endgroup\$ Commented Nov 3, 2017 at 12:05
  • 1
    \$\begingroup\$ 555 will probably not do, for a reasonably accurate 10 minute delay. \$\endgroup\$
    – user16324
    Commented Nov 3, 2017 at 12:05
  • 1
    \$\begingroup\$ A 555 astable could do this. But what time precision do you need? Would you accept differences of about 30 sec in the timing (9:30 to 10:30)? If you need exactly 10 minutes, it will be very difficult to tweak 2 resistors and one capacitor, it will take too much time to adjust the timing of each single board. Even if time and cost are constraints, you should go for a mc, as ATTiny. The price of the main component is not the only thing in a design's cost. The 555 IC needs extra components, the design will not be so easy, and after all you'll spend more time building, testing, adjusting. \$\endgroup\$
    – mguima
    Commented Nov 3, 2017 at 14:08

1 Answer 1

1
\$\begingroup\$

Consider a "precise timer", which does some of the temperature compensation for you: https://www.e2v.com/shared/content/resources/File/documents/QP_semi/NSC_LM122.pdf

Or http://www.reuk.co.uk/wordpress/electronics/making-very-accurate-timers/ offers this schematic: enter image description here

\$\endgroup\$
1
  • 1
    \$\begingroup\$ +1 for an answer that provides what the OP asked for. But the number of external components indicates that the OP should go for a microcontroler. \$\endgroup\$
    – mguima
    Commented Nov 3, 2017 at 16:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.