problem with 555  - Page 1
Forum section: electronics / projects

author: navidrct
author_rank: Regular Contributor
timestamp: June 11, 2015, 01:23:37 pm
content: hiin astable mode of 555 i have square wave of 50% duty cycle.i WANT TO use it for measure L of inductor but when i place my inductor ,square wave is gone.why this is happening?

author: navidrct
author_rank: Regular Contributor
timestamp: June 11, 2015, 01:36:30 pm
content: this is the circut. remeber rest of circut is in astable mode

author: matseng
author_rank: Frequent Contributor
timestamp: June 11, 2015, 01:40:12 pm
content: What's the frequency of the squareware? And what are the values of C1 and L?

author: navidrct
author_rank: Regular Contributor
timestamp: June 11, 2015, 01:46:15 pm
content: 100 KHzC1 is 220 ufL1 is what we want to measure

author: navidrct
author_rank: Regular Contributor
timestamp: June 11, 2015, 02:01:52 pm
content: first pic is one without LC series and another one is when we put LC on output

author: Cliff Matthews
author_rank: Unknown
timestamp: June 11, 2015, 02:53:40 pm
content: I remember getting help on a similar issue - the members here are very helpful.http://seventransistorlabs.com/tmoranwms/Elec_Inductor.htmlFrom Tim (IMHO best forum guru, but put on your thinking cap..)http://www.tek.com/document/application-note/capacitance-and-inductance-measurements-using-oscilloscope-and-function-geFrom Tektronicshttp://ludens.cl/Electron/lmeter/lmeter.htmlExcellent builder

author: matseng
author_rank: Frequent Contributor
timestamp: June 11, 2015, 03:03:42 pm
content: What did you expect to happen? To get a squarewave with a different frequency? Since the frequency is fixed by the other parts connected to the 555 that will not happen.In very simple terms the squarewave at the output will be "distorted" into another shape by the load caused by the charging/discharging of the of the capacitor as well as the buildup/teardown of the magnetic flux in the inductor. So what you see is probably correct, but how you should interpret the new curve to calculate the value of the inductor I leave to someone else - preferably the person that created the circuit you've built.

author: w2aew
author_rank: Super Contributor
timestamp: June 11, 2015, 03:19:13 pm
content: You can try using this method. It *requires* that the signal source has a *low* output impedance, and can tolerate short-circuit to ground.

author: navidrct
author_rank: Regular Contributor
timestamp: June 13, 2015, 04:46:49 am
content: Quote from: w2aew on June 11, 2015, 03:19:13 pmthanks

author: navidrct
author_rank: Regular Contributor
timestamp: June 14, 2015, 07:05:29 am
content: its full circut in attachment.why this is happening?

author: MrAureliusR
author_rank: Unknown
timestamp: June 14, 2015, 10:02:19 am
content: You are aware that you've essentially created an LC filter? I'm not really sure if what you're doing will work well for measuring inductance... But I'm totally willing to be corrected.You have to remember that an inductor's impedance is very frequency dependant. Depending on the frequency, it has less and less impedance, so at lower frequencies you might be loading the output of the 555 a lot. But again, greater minds than mine can probably figure this out.EDIT: Also remember that some diodes can take longer to 'turn on' than others, possibly causing that large spike before they are able to clamp to the rails.

author: navidrct
author_rank: Regular Contributor
timestamp: June 14, 2015, 10:22:48 am
content: Quote from: MrAureliusR on June 14, 2015, 10:02:19 amthanks i hope sombody tell me why internal resistance of voltage sourcce can effect this much on signal?