Telephone in use indicator (CB9467E)

We found this circuit in a Hands-On Electroncs from the 90s. The circuit uses an LED indicator. Diodes are general purpose types.

| Clique na imagem para ampliar |

Beep For Flasher (CB4340E)
This circuit adds a beep to turn on with car flashers that do not have this feature. A 47 ohm to...
TTL Oscillator (CB15741E)
Depending on the value of C1, this oscillator can produce signals of up to 1 MHz. For a capacitor of 10...
Hearing Aid Amplifier (CB18574E)
This commercial circuit, sold under the designation H531 in Japan in the 1960s, used three...