how to measure frequency in this circuit?

i want to measure the frequency of this flasher circuit but i always get a frequency close to that of the mains. I am using a wall wart.
i changed some of the components to speed up the flashing but the frequency reading stayed the same.
to check my multimeter i tried measuring the frequency of mains and the joule thief circuit and it looks like my multimeter is good.

how should i measure the frequency in this flasher circuit?

Picture of how to measure frequency in this circuit?
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MarkP642 years ago

Sorry to add a comment on an incredibly old thread, but
could someone please help determine how to calculate the frequency of the
flashing LED in this circuit diagram?

I would have thought it was something like
0.693*330,000*.00001 = 2.28 flashes/seconds.

But when I make this circuit in Yenka, it comes out to be
more like 1 flash/second.

There is a very similar circuit at the following website
with an explanation of how the circuit works but no timing calculations.



lemonie6 years ago

How are you measuring ~60Hz then?

codestroy7 (author)  lemonie6 years ago
i measure the frequency across the LED and it always give 60Hz

How? You've asked how to measure frequency, but you say that you're already doing it. Do you doubt that the measurements which you get are correct?

Re-design6 years ago
Change to battery then measure again.
codestroy7 (author)  Re-design6 years ago
I'll try that.
Get yourself a cheap oscilloscope - you really can't do serious work without one eventually.
Aren't cheap and oscilloscope mutually exclusive? :-)

Although I was able to sort out my RC transmitter with a free offering using the PC sound card. Seemed to work within it's abilities. Not much bandwidth though.
Things have got better now even I could afford that.
rickharris6 years ago
Across the LED should give you a realistic reading but you can work it out.

The frequency is controlled by the capacitor and the resistor that discharges/charges it.
codestroy7 (author)  rickharris6 years ago
yah i know... the circuit is working...

i tried to get the frequency across the LED but i get nearly 60Hz which is impossible since the LED is not visually flashing that fast i suppose i am getting the frequency of the mains.

at some point i changed the flashing speed of the LED so i am expecting a change in the frequency reading. but the reading is still 60Hz
Add a smoothing capacitor - your 'dc' wall wart is spitting out bumpy dc with ripple, and your meter is detecting that ripple.
codestroy7 (author)  frollard6 years ago
thanks i'll try that.