555 Beating Heart 4 Valentine

192

02:25:08

Basic 555 but signal is tapped at Threshold. Signal reduced by 1M resistor to remove interference with IC, reamplified by a Darlington arrangement.

published 11 years ago

hurz

11 years ago

Ok, but this way it depends only on Hfe of your transistors. Suppose you build it with 2 BC548B it Hfe would be more around 200 or 300 instead of EC default 100. Both Hfe would be multiplied and the LED would even go off. Try here on EC and change Hfe. Because you drive it only by current. And be aware Hfe also changes a lot over temperatur. So this way can only work if you measure the Hfe and than customize the base resistance and keep the bjts on stable temperatur. Solution would be to first place a voltage follower and after that adaption for the LED voltage/current. Keep it up

Karlberg

11 years ago

Hurz >> Good advice. Thanks 😺

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