Complete fiber optic systems are finding widespread use in all types of applications figure 1 provide a very simple fiber optic telemetry system using NE555 that can be used in a variety of telemetry application essentially. The transmitter is an astable oscillator using the popular NE555 (IC1).
Circuit Diagram of Fiber optic telemetry system Using NE555
The variable resistance LDR1 contract the rate of the pulse applied to the LED. LDR1 can be any variable resistance transducer such as a strain gauge for pressure sensing, a thermistor for temperature sensing, or a photoresistor for light sensing. It could also be a carbon microphone to transmit audio information. The transmitter is essentially a voltage to frequency (V/F) converter, and thus any of the IC (Voltage to frequency converter) chips (such as the LM331) could be used in this application.
The receiver circuit is shown in figure 1 used as MC 1458 (IC2) dual op-amp as a preamplifier (first op-amp) and as a comparator (second op-amp). Once the receiver pulses and cleaned up by the comparator, they are applied to the IC3 (NE555) used as a frequency to voltage converter. Adjustment of VR1 controls the threshold level of the comparator, while VR2 permits calibration of the output meter. The simplicity of this system makes it easily adapted to a variety of applications.
PARTS LIST OF FIBER OPTIC TELEMETRY SYSTEM
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1 = 1 KΩ
R2, R3 = 100 KΩ R4 = 1 MΩ R5, R6, R8 = 5 KΩ R7 = 10 KΩ VR1, VR2 = 10 KΩ |
| Capacitors |
| C1, C5 = 0.22 µF (Ceramic Disc)
C2 – C4,C6 = 0.1 µF (Ceramic Disc) |
| Semiconductors |
| IC1, IC3 = NE555 (Timer IC)
IC2 = MC1458 (General Purpose Operational Amplifier) LED1, LED2 |
| Miscellaneous |
| LDR1
M1 = 0-1mA ammeter Optic Cable |