4017 output triggering - Page 1
Forum section: electronics / beginners

author: Bigkim
author_rank: Contributor
timestamp: February 18, 2024, 10:42:35 pm
content: If I have 2 individual 4017 I.Cs being driven by 555s, how do I activate a buzzer for 3 seconds when both the outputs land on a specific output. (EX. when both leds that are on output 5 are illuminated)??Thank you for any help

author: Ian.M
author_rank: Super Contributor
timestamp: February 18, 2024, 11:55:57 pm
content: A diode from each to the /RESET pin of another 555, cathode towards the 4017 output + a pullup resistor on /RESET, so the 555 is held in reset until both 4017's outputs are high. Configure the 555 as a monostable, with 3 second period.

author: pqass
author_rank: Super Contributor
timestamp: February 19, 2024, 12:44:47 am
content: See attached schematic andsimulation here.Notice, I've stopped the 1st 4017 (CE pin=H) just so the 2nd one will trigger the one-shot.Adjust RC values on one-shot for 3 seconds . Seeherefor the formula/calculator.You will need to replace the one-shot output LED with a buzzer (and possibly a transistor to activate it).

author: Ian.M
author_rank: Super Contributor
timestamp: February 19, 2024, 01:41:29 am
content: Pqass's version with a transistor inverting the diode AND output to drive Trigger is preferable if you want the buzzer to continue till the 3 second timeout even if one of the 4017 outputs goes low earlier than that. If however you want the buzzer to cease either at the timeout or when one of the 4017s outputs goes low, here's how to implement my suggestion.

author: Bigkim
author_rank: Contributor
timestamp: February 19, 2024, 03:56:46 am
content: THANK YOU for your response.My concern is that this will trigger whenEITHERof the selected outputs on the 4017s illuminates.....where as I want it to trigger only whenBOTH SELECTED LEDSilluminate at theSAME TIME

author: Bigkim
author_rank: Contributor
timestamp: February 19, 2024, 03:59:08 am
content: THANK YOU for your response.My concern is that this will trigger whenEITHERof the selected outputs on the 4017s illuminates.....where as I want it to trigger only whenBOTH SELECTED LEDSilluminate at theSAME TIME

author: pqass
author_rank: Super Contributor
timestamp: February 19, 2024, 04:40:35 am
content: If the 4017 output with the diode cathode facing the pin is HIGH then the diode is reverse biased (not conducting). If BOTH (one from each 4017) are reverse biased at the same time, this gives the opportunity for the pullup resistor to turn on the transistor which then grounds the 555 trigger pin momentarily (for the maximum duration of when both pins are HIGH). When a 4017 output is LOW, which is normally the case for all but one output, then at least one of the diodes (which are now forward biased) will keep the transistor off.With minor update to the original schematic below andsimulation.Added LEDs for chosen outputs, removed unneeded base resistor, and raised pullup.

author: Bigkim
author_rank: Contributor
timestamp: February 19, 2024, 03:23:27 pm
content: ~One final question...So if lets say Q4 LEDoneachis Illuminated, it will only then trigger the 555?

author: pqass
author_rank: Super Contributor
timestamp: February 19, 2024, 03:33:18 pm
content: Quote from: Bigkim on February 19, 2024, 03:23:27 pmWith reference to my schematic, NO.Since the 2nd 4017 Q1 output is off thus grounding the transistor preventing it from triggering the 555.Only when the 1st 4017 Q4 and 2nd 4017 Q1 are BOTH HIGH, will the transistor turn on and trigger the 555.Lookupdiode logic (wired AND).

author: Bigkim
author_rank: Contributor
timestamp: February 19, 2024, 06:18:48 pm
content: Im having a problem that when any 1 led matches on either of the boards there is a triggering, of the circuit, altho I have hooked this up to Q3 only on each board

author: pqass
author_rank: Super Contributor
timestamp: February 19, 2024, 06:57:48 pm
content: Quote from: Bigkim on February 19, 2024, 06:18:48 pmAre the selection diode cathodes facing a 4017 output pin?If yes, confirm wired-AND is working by temporarily removing the transistor and replace with a LED (anode where the base lead was and cathode to ground). You may need to replace the 10k pullup with a 1K or the LED may be too dim to see. Confirm that this arrangement causes the temporary LED to light when both chosen 4017 outputs are HIGH. We'll debug further once you confirm.

author: Bigkim
author_rank: Contributor
timestamp: February 19, 2024, 09:07:40 pm
content: everything seems to be correct

author: pqass
author_rank: Super Contributor
timestamp: February 19, 2024, 10:02:02 pm
content: Quote from: Bigkim on February 19, 2024, 09:07:40 pmSo everything working as expected then?