This unusual circuit from a Popular Electronics of the 90s uses LED indicators, operating as a bridge. The components used are common. It is based on the tuning of the signal by a PLL.
We found this circuit in a 1975 publication. The circuit can be made with BC548 transistors for...
This circuit was found in the December 1992 Radio Electronics magazine. Range depends on optical...
This circuit is from the National Semiconductor CMOS manual of 1977. What this circuit does is to...