This is a motor speed controller circuit diagram built based Maxim MAX4295. This with this circuit you will be able to control the speed of motor rotation.

Resistor R1 biases the potentiometer to match the input range of U1. Full counter-clockwise rotation of the pot corresponds to maximum-speed reverse rotation of the motor. Mid-scale on the pot corresponds to motor off, and full clockwise rotation of the pot produces maximum-speed forward rotation in the motor.

A multivibrator is an electronic circuit used to implement a variety of simple two-state systems such as light emitting diodes, timers and flip-flops. The monostable multivibrator will create a condition: in which one of the states is stable, but the other is not—the circuit will flip into the unstable state for a determined period, but will eventually return to the stable state. Such a circuit is useful for creating a timing period of fixed duration in response to some external event. This circuit is also known as a one shot. A common application is in eliminating switch bounce.

Component:

C1_______ read the diagram
C2_______ 10nF
IC1______ LM555

This a two station intercom. It uses two wires to run between each intercom unit. Each is self contained with its own battery, speaker, microphone and amplifier circuit.

An LM386 audio power amplifier is used. It is widely available, used a minimum of external parts and is well suited to battery operation. It will give just over 1W into the 8 ohm speaker. The gain can be varied by the external components attached to pins 1 and 8. Gain can range from 20 (open circuit – pins 1 & 8 not connected) to 200 (pins 1 & 8 short circuited).

Here the low resistance connection tester which can be used as cable or wire tester, soldered joints and other types of connection with resistance value between 0.25 and 4 ohm.

Notes
This simple circuit uses a 741 op-amp in differential mode as a continuity tester.