OPTOELECTRONICS
This section describes building the optoelectronic sensor that can be used to give an idea of the speed of the engine. The circuit in basic terms uses an Infra Red Emitter and Photo Transistor combination to generate pulses. The pulse is generated when the signal from the emitter is reflected back to the Photo Transistor. To do this a white bar is placed on the rotating object (clutch bell housing) and the rest of the object painted matt black. Each time the white bar rotates past the emitter the signal is detected by the Photo Transistor. The use of an OP Amp (CA3140E) produces a clear signal that can be passed through a 555 timer circuit (monostable) to generate a clear single pulse used in the final logic configuration of NAND gates (74LS00). To generate the correct timing sequence a 555 timer (astable) feeds a pulse into the NAND gates to accept X seconds worth of pulses from the sensor. The value of X can be adjusted using the Variable resistors in the 555 clock circuit. The result is a number of rotations is displayed on the digital counter module for the set value of time, use of the reset line will reset the counter after each value is displayed giving a new measure of revs per unit of time. Although not 100% accurate if the value of time can be set at 1 sec then the value of the counter display needs to be multiplied by 60 to get RPM! It sounds complicated but it does work honest!
On first assembly the circuit failed to trigger the counter which we put down to the amplifier circuitry and having used the old fashioned pins in a board method of building the circuit we went for Tracktronics tape the next time. Success, this time the counter gave a value of pulses each time a white bar was seen. Use of a TV remote also generated pulses that gave varying values on the display. Each element of the circuit is drawn below and it is easier if using the tracktronics tape method to do this, as problem solving pupil soldering mistakes is easier! We hope to develop this further to a PCB design in the future but not having etch facilities at present we have not gone down that avenue and although the finished article may look a bit Bulky it does the job!
The Power Supply 5 Volts
The Opto Sensor Circuit.
The Monostable 555 Timer Circuit (pulse shaper).
The Astable Clock 555 Timer Circuit.
Logic Gate Circuit.
Power Supply for Digital Display.
Order Kit List From Rapid Electronics.
|
Component Name |
Order Code |
Quantity |
Price £ / Unit |
|
Digital Counter |
48-0500 |
1 |
9.20 |
|
78L05 Voltage Regulator |
47-3278 |
1 |
0.24 |
|
NE555 Timer IC |
82-0336 |
2 |
0.22 |
|
74LS00 Quad 2 Input Pos NAND Gate |
83-0526 |
1 |
0.22 |
|
CA3140E Single MOSFET OP Amp |
82-0688 |
1 |
0.452 |
|
BZYC3V0 Zener Diode |
47-3002 |
1 |
0.06 |
|
BP103B Phototransistor |
58-0490 |
1 |
0.50 |
|
SFH485 IR Emitter |
58-0445 |
1 |
0.29 |
|
270R Resistor Red Violet Brown |
62-0356 |
1 (pack of 100) |
0.60 |
|
1K Resistor Brown Black Red |
62-0370 |
1 (pack of 100) |
0.60 |
|
4K7 Resistor Yellow Violet Red |
62-0386 |
1 (pack of 100) |
0.60 |
|
10K Resistor Brown Black Orange |
62-0897 |
1 (pack of 100) |
1.20 |
|
100K Resistor Brown Black Yellow |
62-0964 |
1 (pack of 100) |
1.20 |
|
1M Resistor Brown Black Green |
62-1012 |
1 (pack of 100) |
1.20 |
|
2M2 Variable Pot |
65-0650 |
1 |
0.41 |
|
100K Variable Pot |
67-0245 |
1 |
0.10 |
|
1nF Capacitor |
10-3200 |
1 |
0.07 |
|
10nF Capacitor |
10-3210 |
2 |
0.07 |
|
22nF Capacitor |
10-3214 |
1 |
0.07 |
|
100nF Capacitor |
10-3220 |
3 |
0.08 |
|
470nF Capacitor |
10-3228 |
2 |
0.18 |
|
Low Profile Dil IC Socket 8 pin |
22-0150 |
3 |
0.05 |
|
Low Profile Dil IC Socket 14 pin |
22-0155 |
1 |
0.08 |
|
Tracktronics Tape |
34-0635 |
1 |
3.95 |