Darkroom-enlarger-timer


Posted on Nov 28, 2012

The NE555 circuit is a basic one-shot timer with a relay connected between the output and ground. It is triggered with the normally open momentary contact switch, which when operated, grounds the trigger input at pin 2. This causes a high output to energize Kl which closes the normally open contacts in the lamp circuit. They remain closed during the timing interval, then open at time out. Timing is controlled by a 5-M!lpotentiometer, R,. All timer -driven relay circuits should use a reverse clamping diode, such as D 1, across the coil.


Darkroom-enlarger-timer
Click here to download the full size of the above Circuit.

The purpose of diode D2 is to prevent a timer output latch-up condition in the presence of reverse spikes across the relay. With the rc time constant shown, the full-scale time is about 1 minute. A scale for the 5-M!l potentiometer shaft position can be made and calibrated in seconds. Longer or shorter full-scale times can be achieved by changing the values of the rc timing components.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Oscilloscope 4 Channel Adapter
Mixers and oscillators
Fire Alarm Circuit using LDR (Light Depending Resistor)
Ultrasonic Mosquito Repeller Circuit Using CMOS IC
resistance Replicate thermistor behavior for second sensor
Evaluation Board For Single Supply 12-bit 500 Ksps Adc
3.3V and 5V DC DC converter circuit design using LT3692 DC converter dual tracking regulator



Top