Problem with 555 circuit - Page 1
Forum section: electronics / beginners

author: nikkoderic
author_rank: Contributor
timestamp: October 29, 2016, 03:08:43 pm
content: I am attempting to follow this project regarding testing power inductors.http://elm-chan.org/works/lchk/report.htmlAnd this is the circuit diagramhttp://elm-chan.org/works/lchk/lchk_sch.pngBut I am having problems. The first 555 chip does not produce any output. I also tried it in the simulation and it also does not work either. There seems to be a mistake in the circuit.I looked for other similar project and I found this one.https://ludens.cl/Electron/lmeter/lmeter.htmlAnd here is the circuithttps://ludens.cl/Electron/lmeter/LMETER.pngIt seems to be using the same 555 circuit. I dont really understand whats happening. Can someone explain?

author: Andy Watson
author_rank: Super Contributor
timestamp: October 29, 2016, 04:15:14 pm
content: The circuit looks reasonable. Is the output of the 555 stuck high or low?Note the pins on the circuit diagram are (misleadingly) not shown in true physical position. However, the pin numbers are correct.

author: Algojervia
author_rank: Unknown
timestamp: October 29, 2016, 04:57:24 pm
content: Yeah they took some artistic freedom there with the pin arrangement, be aware.What simulation are you using? I recently tried to simulate a 555 based circuit in the online Falstad simulator and could not make it work even thou it worked on the breadboard.

author: StillTrying
author_rank: Super Contributor
timestamp: October 29, 2016, 06:00:15 pm
content: Quote from: nikkoderic on October 29, 2016, 03:08:43 pmThe 1st 555 works exactly as I would expect in LTspice, oscillates at 400hz producing very narrow lows of about 150ns, which might be too narrow as triggers for the 2nd 555.Putting 1k in series with the Discharge pin widens them to 860ns.

author: nikkoderic
author_rank: Contributor
timestamp: October 30, 2016, 01:40:40 am
content: Actually, the first 555 does produce very narrow lows in the simulation using Multisim. Thats really weird if it was really designed that way. Is it a good design?I tried powering up the first 555 in an actual circuit without connecting its output to the second one. But i got confused because it only outputs HIGH on the oscilloscope and thats why i posted here. The pulses are probably too narrow.Right after I posted this question, i tried hooking up the output to the second 555 and it now seems to be working fine because the pulse width changes when i turn the pot. But it seems that the ON time is too short compared to the OFF time, guess ill have to check.

author: StillTrying
author_rank: Super Contributor
timestamp: October 30, 2016, 02:58:07 am
content: As long as the trigger pulses get very close to 0V they can be less than 100ns, according to an old NS data book.The current pulses to the DUT can be up to 60 Amps, so they will be quite short lived one way or another!

author: nikkoderic
author_rank: Contributor
timestamp: October 30, 2016, 07:03:31 am
content: I dont know what happened last night but I can finally see the short LOW output now. My scope probably was not able to trigger before. I really thought there was something wrong because the site stated that I should be expecting a 50hz output.Yeah I just realized that it makes sense having only short pulses, knowing that the current will ramp up quickly.Ok, i'll proceed then. Thank you. =D