555 timer. Keep a LED off for 60 seconds than on for 2 seconds

Thread Starter

Senaph

Joined Apr 24, 2019
2
I need to use a 555 timer (astable) mode to keep a LED off for 60 seconds than on for 2 seconds, a bit smoke detectors that turns a red LED on about every 60 seconds for 1-2 seconds then repeats. If it is easier to turn the LED on for 60 seconds and off for 2 seconds it won't be problem as I can invert pin 3 from the 555. I'm using a breadboard. a circuit diagram would be greatly appreciated.
 

danadak

Joined Mar 10, 2018
4,057
Possibly for future reference this uses mBlock to generate code for Arduino
type board/part.

You drag and drop functional blocks, config them, and mBlock generates the code to put
into the micro. Lots of how to videos on web, 6'th graders writing code this way to control
basic robots.

You could use a nano board, ~ $3, or an ATTINY85 chip. The former programs right off USB
with mBlock. The latter uses an Arduino board to program the 8 pin ATTINY85.

https://www.banggood.com/ATmega328P-Nano-V3-Module-Improved-Version-No-Cable-Development-Board-p-959231.html?gmcCountry=US&currency=USD&createTmp=1&utm_source=googleshopping&utm_medium=cpc_elc&utm_content=frank&utm_campaign=pla-mix-us-pc-0626&gclid=EAIaIQobChMI0KbC4cO26AIVkYrICh3VWA-uEAQYByABEgIWRfD_BwE&cur_warehouse=CN

This example does what you want.


1585170283224.png


Regards, Dana.
 

Dodgydave

Joined Jun 22, 2012
9,205
Use an hysteretic astable circuit using the 555, with steering diodes for charge and discharge, .
 
Last edited:

danadak

Joined Mar 10, 2018
4,057
1585173220206.png
The above is the ATTINY85 approach. Added is a pin that tells micro to disable LED
blinking. You would have to add the block code to mBlock to facilitate the disable
function.


Regards, Dana.
 

dl324

Joined Mar 30, 2015
10,946
This should give 60 64 seconds on, 2 seconds off:
1585174072230.png

If you drive the cathode of with the output, you can get LED off 60 64, then on 2. If the output of the timer isn't high enough to turn the LED off, add some signal diodes between the cathode and output.

Intervals will be affected by component tolerance and cap leakage.
 
Last edited:

danadak

Joined Mar 10, 2018
4,057
You say that timing accuracy not an issue. So if it blinked at a 10 second rate, or a 100+ second rate,
vs the 60 sec target, you would be OK with that ?

LM555 timers using large caps and high valued R's really sloppy in timing, due to cap tolerance,
leakages in LM555 and cap, LM555 trigger accuracy, temp drift. You could of course take care of that
with trim pots, but thats not very elegant.

Just a thought.

The accuracy with a NANO < 1% over T and V, an ATTINY85 w/o crystal ~ 2 - 3 %.


Regards, Dana.
 

Bernard

Joined Aug 7, 2008
5,555
In selecting timing parts , depends on what you have on hand. I would select C around 100 uF with leakage of 10 M or better. R then in 1M range. Leakage does not seem to be proportional to capacity, a 10 uF measured 500 k & a 10,000 uF measured 21 M. My longest timing with a 555
was 3 hours +- about 10 min.
 
Top