A very simple DC motor speed controller circuit can be constructed using a LM317 voltage regulator integrated circuit . This DC motor speed controller can be used for speed control of mini drills or for other small DC motors . This motor controller circuit will provide a large output current . The maximum output current from the secondary turns of the transformer shout provide 1.5 times of the maximum DC output current . The output voltage and the speed ( rpm ) is set by the P2 variable resistor .
As soon as the current drawn exceeds a certain value , T2 will be switched on . This results in a base current for T3 so that R5 is in parallel with R6 . This automatically raise the output voltage to counter a threatened drop in rpm . The moment at which this action occurs is set by P1 .
This electronic schematic circuit is a very simple two way electronic intercom circuit based on a LM386 audio amplifier circuit . The electronic intercom schematic use two separate LM386 circuits one amplifier for each station .
The LM386 based intercom electronic circuit operate as two separate entities with switches at either station controlling which will transmit or receive . The value of the capacitors from the electronic schematic are in microfarads .For this intercom circuit you can use a 8 ohms speaker , one for each station . The intercom circuit require a 9 volts dc power supply . With the C7 and C8 capacitors connected in the circuit the amplifiers provide a high gain around 200 and without these two capacitors connected in the circuit , the gain drop s around 20 .
This road ice alarm electronic circuit schematic use a LM3900 quad operational amplifier . As a temperature sensor this road ice alarm circuit use a thermistor . When the temperature is around 36 degrees Fahrenheit (2.2 celsius degrees ) the LED connected on pin 4 at the LM3900 op amp will flashes at once about each one second . When the temperature is going down to 32 degrees Fahrenheit (0 degrees Celsius ) the led remains on . Before you use this road ice alarm electronic circuit you need to calibrate it . To calibrate the circuit you need to put the thermistor in a mixture of a crushed ice and water and adjust the variable resistor R2 until the LED is remaining on . The road ice alarm circuit needs to be powered from a 12 volts DC power supply circuit ( If you use it for car the car battery can be used for powering the circuit ) .