10 Minute UV Dental Tooth Whitener Timer

Project Description

Lets get onto the circuit

Figure 2  Circuit View

The circuit is all based round the 12f675 and uses timer interrupts a button switch for detecting when the unit has been started to start the timing sequence The Unit must also beep at start up and count to 9 seconds keeping the Luxion led on During the last minute the Module must beep once per second during the final minute countdown so as to notify the nurse that the exposure is complete this must be done via a buzzer emitting a high pitched beep

Figure 1  PCB Image view

The circuits is very easy to understand

D2 ensures Reverse polarity protection With F1 being rated at 500ma to protect the rest of the circuit D1 is a 5v1 zenor diode rated at 500mw which is purely there to prevent over voltage protection c4 decouples the 12F675 recommended in the data sheet as close as you can to pins 1 and 8 R2 to R5 limit the current through the Luxion Led which is switched on via the FET an 1RF540 biased off via R6

R6 and R7 form the biasing network via GP1 of the CPU turning on the Fet and of course the Luxion R1 and R10 form a potential divider for the switch which activates the timer sequence so that countdown can begin when this starts the Luxion Led is turned on at the end of the final countdown I.E 10 minutes then the Luxion LED is subsequently turned off Switch sensing is done via GP0 which is de bounced when finger press of the switch is released GPO looks for a logic High to start the timer sequence and is held low when no press is detected

The buzzer sound is sent via GP2, R9 which forward biases Q2 using a PWM waveform hence our sound of the buzzer

The code is written In C I used the boost C compiler to achieve this

Website below “Very Good C compiler also available from Maplin’s UK “
http://www.maplin.co.uk
http://www.sourceboost.com/

The CPU uses as Timer interrupt procedure to count the number of milliseconds obviously upwards for number of seconds increments seconds each time the seconds reaches 60 and then obviously minutes

When the minutes has reached 9 the sound function is called once every second for the final minute

The whole process is maintained in the main method calling an Init function so as to set up the CPU ports and disable other features such as the Ansel register

You can find more detail on this in the data sheets to gain a full understanding of how the registers work

Switch press is checked then sets a flag if pressed and then start the interrupt procedure when the timer overflows each time the timer overflows you can then see what happens to the milliseconds , seconds and minutes

I’ve included all plots etc PCB layouts for you in the files that you might want to download You could if you wanted to simply change the values in the C code to turn this into a 3 minute Egg timer

I hope this proves useful to many a dental nurse who needs such equipment but has limited cash flow

The design has been fully tested so its all ready to go Hope this really helps some of you

Mark Harrington

Project Files