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# Problem with measuring the output frequency of NE555 circuits

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#### Deese

##### Newbie level 2
I am having a problem measuring the Hz output of my 555 circuits.I have a fluke 88 multimeter,it has hz,and duty cycle functions.The problem I am having is that when I touch the leads I get a reading like 60Hz or so for 1 second then the meter reads zero.But my frequency is nowhere near 60Hz in the first place.Sometimes I get a Hz reading while touching only one lead of the multimeter to the output of the 555.Is this a common problem with these or could my meter be overloading the 200ma rating?I wouldnt think so but I am not an expert either.Any help is appreciated.

Re: NE555 Timer Problem

If it is in the mA range you are measuring propably you short the 555 with the low resistance of the meter.
Measure in the specified Frequency scale if exists in the Fluke88 or in the AC volts range.

It is important to use a battery for the supply of your circuit (555) so as to avoide any hum noise from the mains (50 Hz from the mains supply).
Also, use a load resistor at the output of the 555 of approximately 100-300 Ohms so as to minimise any mains 50Hz pick-up (interference).

Some multimeters need few volts at their input lead in order to be able to measure the frequency correctly (input sensitivity of meter in frequency scale), something more than 1 volt.

Re: NE555 Timer Problem

what is the frequency and duty cycle that you have design your circuit for???

Re: NE555 Timer Problem

Thanks for the info,that could be the problem because on another circuit I have I used a transistor that didnt have enough gain and it wouldnt switch it unless I used a 100 or 200 ohm resistor between the output and the base.I am going to get back in the shop today and check it out. To answer the question,this circuit is supposed to me a test circuit for me.I used a IC socket so I can remove the 555 chip easily,I set it up for wide duty cycle range astable with a 50k pot and a 3k resistor on the wiper so at either end of the range can never be less than 3k resistance.I put a terminal block on the board connected to pin 2/6 and to ground so I can change out the timing cap quickly without soldering,I am using a 10n presently.Which makes the Hz around 2.5Khz so says my 555 timer pro.And I think it will shift from about 5% to 95% duty cycle

Re: NE555 Timer Problem

Bell book about pulse techniques is a good reference in this filed

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