How it works
How dive tracker scout transmitter works
All codes with letter# (Ex P2) make reference to locations on circuit board. Power is connected to P2. D4 is there to prevent damage to the board when power is connected backwards.
VBAT is the power net used to supply power to those things that require battery power such as U1 the voltage regulator.
When S1 is shorted VBAT is allowed through S1 and D1 to U1 pin3. This allows the voltage regulator to generate VCC. The voltage regulator will generate power as long as U1 pin3 stays high. This happens when the processor gets VCC and starts processing instructions. The instructions tell U2 pin5 to go high and stay that way. Now the switch no longer needs to stay shorted to keep the unit on.
While the magnet is holding on the unit, it performs a low battery test. Pin6 of U2 will go high and low. This turns the led on and off. When the battery is low this causes high - low action to increase, so the led will blink faster. The processor can tell if the battery is low by measuring the battery voltage at U2 pin 4. This processor has an analog to digital converter built into it. This means analog signals are turned into digital readings. R4,R7 and R8 divide the voltage making it fit within the rails of the analog to digital converter.
When the magnet is released the unit will go into standard operation. This means the unit will transmit. When the unit transmits the led will also blink with each pulse.
The unit transmits by toggling U2 pin 7 72K times per second for 4 milliseconds. The pin then goes low for 300 milliseconds and then repeats the cycle. This toggling of the line controls the switching action of Q1. When Q1 senses a voltage greater than the voltage seen on the source it allows the source to flow through the drain and to ground. This allows voltage to move through the transformer connected to P1. A magnetic field is then generated when the voltage potential at the gate becomes less then that on Q1 the magnetic field collapses. When this happens an elastic effect tales place creates very large voltages (Transformers are used to increase and decrease voltages and the current). The higher voltage goes to the sonar transducer, which expands and contracts when the voltage comes and goes. This fast expanding and contracting sounds like little snaps, which is the sonar ping.
All digital processors need a clock of some sort. Processors use the clock to process instructions. Our clock is connected to U2, which is a PIC12C672 and is sensed by pins 2 and 3.
When the unit is to be turned off U2 pin 5 goes low and the shut down line on the voltage regulator goes low. The shut down happens when S1 is shorted again and the processor senses a high on U2 pin4. This stops the generation of VCC. You will now need to short S1 to turn the unit back on.
How dive tracker scout receiver works
Power is connected to P2. There is no diode in this circuit to protect it from having power connected backwards. Everything connected to VBAT is connected directly to the battery. If power is connected the wrong way around those parts will get hot. Set the supply voltage to 3.6 volts and the current to 100 milliamps. If the board is working it will consume no more than 50 milliamps. Apply power to be connected to P1.
U1, which is the voltage regulator (max8873) now, has a supply voltage. When S1 is shorted VBAT will flow through the switch and D1 to the power on line of U1 pin 3. This allows the voltage regulator to generate VCC. The processor then receives VCC, which allows it to power up and process instructions. Note that the processor use’s an internal R/C circuit as a clock. One of the first instructions tells the processor to set U2 pin5 high. This sets pin U1 pin3 high so the switch no longer needs to be set high.
While the switch is set high and the processor has been has waken up the unit will perform a self test. The self test runs as long as the switch is shorted. The unit tests the filter and the battery. If the unit fails to stop testing you may have a short on pin 4 of U2. If the filter is working both the red and the green LED’s that are next to each other will blink at the same time. If you see any other pattern you have a problem. The other LED that sits by itself indicates how much battery life is left in the battery. A fast blink indicates a low battery and a slow blink indicates a good battery. If the LED’s fail to blink look on pins 2, 3, and 6 of U2. They should go high and low. If not look to see if there is power. If the low battery led blinks and not the others look to see if pin 7 U2 is toggling. If it does toggle then the processor is programmed for a scout transmitter and needs to be replaced.
Testing the filter. You will want to set the signal generator to 72khz. You will also need to set the pulse rate of the signal generator to transmit the signal for 4 millseconds and stay off for 300 milliseconds. Set the voltage to 1Vp-p. Apply the signal to P1. If the unit is working the green led should blink fast. As you change the amplitude the rate at which the color blinks will change and the color transmitting will change. When the signal is stronger the color will be green as the signal gets weaker it will change to orange and then red. Also the color will blink faster when the signal is stronger for that range.
The signal first goes through two operational amplifiers. These op-amps amplify the signal they also filter the signal so that only the frequency we want goes through. The signal then feeds into a peak detector which turns are ac signal into a dc signal. The processor then reads this dc signal on pin7 of U2. This is an analog to digital converter. It measures the signal and blinks the LED’s accordingly. If you do not get a signal while connected to a signal generator follow the signal through the circuit and see wee it disappears. It will help to make the signal stronger. If you always get the same indication on the LED’s try shorting P1. If you still get the signal measure from pin7 of U2 and work your way back through the circuit. If the signal disappears the problem is between were the signal disappeared and were you last found it.