QUIZ MASTER 3 WITH BUZZER
Price - Stock No
Quizmaster is a device which uses electronics to decide who
pushes their button first, deciding who has the right
to answer the question.
Operation and Testing
This circuit uses three SCR's (Silicon Controlled
Rectifier) to achieve the outcome. An SCR is a diode which only
conducts in one direction, just like a diode - note the A & K
legs. In addition it will only conduct in this direction when it has
been triggered, this is done by applying a voltage to the G leg (Gate). A
SCR will continue to conduct even if the voltage to the gate is removed.
View the Datasheet for the SCR
From the schematic diagram, the 470 R resistors tie the G leg of the SCR's to 0V, preventing a false trigger.
When a button is pressed, the G leg is taken high, the respective SCR conducts, this effectivly connects the A leg to 0V. Current flows from +9V through the LED, resistor and SCR - the LED is illuminated.
As stated before, the A leg of the SCR is taken to 0V, this
has the effect of taking the G leg of the second and third SCR's low
through the 1N4004 diode. This means that even if the second or third
buttons are pressed they cannot trigger their respective SCRs.
The second and third buttons work in the same manor as the first - a totally unbiased 'fastest finger wins'.
Troubleshooting, if necessary will involve careful checking of locations and polarity of components, in particular the diodes and the SCR. Re-solder all joints and check to make sure you have not bridged across between any two adjacent component legs. The end of a broken hacksaw blade sharpened on an emery wheel is a good tool for cleaning between soldered joints.
Contact CdS electronics