Real Beginner lol - And Gate Problem - Page 1
Forum section: electronics / beginners

author: krappleby
author_rank: Contributor
timestamp: March 26, 2020, 10:55:40 pm
content: Hi all,i wrote earlier on about getting a 555 timer to produce two seperate pings five pings after each other, and someone (thank you) showed be the best way to do it..Now, i have 5 brand new SN74LS08 and gates, but they are not working correctly am i doing something wrong..using as an example just one of the and gates, AB and Yif A or B has a pulse, Y has a pulse... (that is not an and that is an or)the second problem is if i have1a 1b and 1y3a 3b and 3yconnected ie using 2 and gates, the if any of 1a, 1b, 3a, or 3b get a ping, both 1y and 3y are providing a ping.am i doing something wrong..i am sending 5 volts into the chip. which is way within the specs of the chip. i have tried tying to ground each of the pins being used, and the pins not being used. but still no luck.. any ideas..5 new chips, all doing the same thinghttp://www.ti.com/lit/ds/symlink/sn74ls08.pdfcheers

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: March 27, 2020, 12:12:43 am
content: Show us your circuit. A schematic is good. Also a picture of your setup and the circuit.Show us how you are driving each input of the gate.What do you mean by a "ping". Is that a normally LOW, HIGH-going pulse? Or a normally HIGH, LOW-going pulse?An AND gate is a NEGATIVE logic OR gate that will transmit a LOW-going pulse on any input as long as the other inputs are steadily HIGH.

author: TerminalJack505
author_rank: Super Contributor
timestamp: March 27, 2020, 12:34:44 am
content: I think it was me that helped you with your earlier question.Given the schematic that I showed you, I have to wonder if you have connected the Vcc and GND pins of the IC. The circuit I showed as a solution to your question didn't show these connections since it was a simulation. This might have lead you into thinking that you didn't need to connect those particular pins.There will also be the question as to what to do with the unused inputs. Someone else might chime-in about that since I can't remember how/if they should be connected for the LS series.Edited to add:The unused inputs can be connected directly to Vcc.

author: krappleby
author_rank: Contributor
timestamp: March 27, 2020, 08:55:34 pm
content: Hi guys, thanks for the replies..Firstly the vcc and gnd pins are connected Lol.Here is the circuit as is regarding the and gate attachedat this moment, a maximum of 5v is being supplied to the VCC pin from a 5v voltage regulatorthe 1a and 1b pins are getting about 3.5v, Which according to the chip details is more than enough to activate them. i have tried tying the 1a and 1b and 3a and 3b down to ground with resistors, but not working eitheras i explained, if the clock pulses in (currently from a 555 timer setup) then both the 1y and 3y outputs go high. on the clock pulse.that is without the 2a and 2b signals.just noticed slight mistake.. There are four decade counters, the CE pin from decade counters, are from your image.. one is set to activate on pin 3 and the other on pin 6. the two clock to decade counters are different counters,so basically based on my previous message, instead of just two signals (one at 1 and one at 5) i have three (one at 1, one at 4 and one at 7) slight modification..cheerskeith

author: Nerull
author_rank: Frequent Contributor
timestamp: March 27, 2020, 09:19:58 pm
content: CE is an input, it can't drive another input.

author: krappleby
author_rank: Contributor
timestamp: March 27, 2020, 09:38:52 pm
content: yes i know.. The CE pin is connected to pin output 4 on the decade counter, so when 4 goes high, it puts CE as high, That signal is also tapped off and sent to the and gate, so when pin 4 is high, and the clock is high, the output on the and gate should be high.

author: krappleby
author_rank: Contributor
timestamp: March 27, 2020, 09:41:20 pm
content: here is the actual circuiti will admit it probably looks terrible lol. but im only a beginner.. lol still working on iti dont know if you can tell, probably but here is what i am trying to do..there are 9 outputs.. each with a led at the moment, as the circuit runs, it will result in a cascade of leds on every 3 leds, and they will flow downwards..so.. 1 4 and 7then 2 5 and 8then 3 6 and 9then repeateach of the leds is connected to a mosfet, which in turn is connected to a high voltage line,so the outcome, is when a led is lit, the mosfet will open and allow a higher voltage to go out to what im working on.