This is really a very simple home telephone ring tone generator circuit which is built with applying only several electronic components / parts. It generates simulated telephone ring tone and requires only DC supply with 4.5V DC to 12V DC voltage. One may possibly use this circuit in ordinary intercom or phone-type intercom. The sound is pretty loud when this circuit is operated on +12V DC power supply. Even so, [...]
The schematic diagram shown right here is the automatic switching-on emergency light circuit which is controlled using IC. The most important capabilities of this circuit are: automatic switching-on of the light on main power failure and battery charger with overcharge protection. When mains electrical power is absent, relay RL2 is in deenergised state, feeding DC source from battery to inverter section via its N/C contacts and switch S1. The inverter [...]
This is the schematic diagram of DC motor speed controller circuit. The circuit applies two oscillators/timers which are connected as a Pulse Width Modulator (PWM). The timer chip which applied in this circuit will be an nmos dual timer/oscillator NE556. This timer IC has two 555 timers in a single 14-pin IC package.