This circuit was obtained in an Electronics World of 1968. The operational amplifiers ones are types of the time, no longer used today. The circuit responds from less than 20 Hz.
This circuit of a few tens of milliwatts of power requires a single source. We found it in a Radio...
This circuit is suggested by Texas Instruments in his Optoelectronics Sourcebook. The transistors...
This circuit used in signaling for boats, cars or barriers was found in a 1980s documentation. It still...