This circuit is from a 1969 EEE magazine. The transistors are from that time, but the circuit can be implemented with modern equivalents, such as 2N2646 for Q3.
We found this circuit in the Linear Applications Handbook published by National Semiconductor in...
In a September 1992 Radio Electronics article, we found this basic 555 circuit used to generate fixed...
In the figure we have a simple way to have a peak bargraph indicator. The amplifier is of the...