This old 4-channel circuit was found in the December 1994 Electronics Now magazine. The circuit uses a 556 as a modulator. Note the code programming key.
An interesting application in case of needing to supply an operational amplifier or a very low...
Found in an old English publication and in other parts of this website in different versions, this...
In the figure we have a differentiator with the LM3900 transconductance amplifier. The circuit is...