# Free Electronic Circuits & 8085 projects

## The production of ultrasonic range finder (regular device)

Published on Mar 16 2011

Presented here do not use a foreign SCM ultrasonic range finder. The ultrasonic range finder, ultrasonic emission by measuring the time difference between the reflected back to the distance measurement and the measured object. Can measure the distance of 0.35-10m. Physical map as follows:

Schematic is as follows:

First, the circuit
An ultrasonic transmitter circuit
Formed by the two integrated circuits 555. IC1 (555) composed of ultrasonic pulse generator, the duty cycle is calculated as follows, the actual circuit components, such as error, there will be some differences.

Condition: RA = 9.1MΩ, RB = 150KΩ, C = 0.01μF
TL = 0.69 x RB x C
= 0.69 x 150 x 10 3 x 0.01 x 10 -6 = 1 msec

TH = 0.69 x (RA + RB) x C
= 0.69 x 9250 x 10 3 x 0.01 x 10 -6 = 64 msec

IC2 composition of ultrasonic carrier signal generator. Pulse signal output from the control of IC1, the output 1ms frequency 40kHz, 50% duty cycle pulse, stop 64ms. Calculated as follows:

Condition: RA = 1.5KΩ, RB = 15KΩ, C = 1000pF
TL = 0.69 x RB x C
= 0.69 x 15 x 10 3 x 1000 x 10 -12 = 10μsec

TH = 0.69 x (RA + RB) x C
= 0.69 x 16.5 x 10 3 x 1000 x 10 -12 = 11μsec

f = 1 / (TL + TH)
= 1 / ((10.35 + 11.39) x 10 -6 ) = 46.0 KHz
IC3 (CD4069) form the first ultrasonic transmitter driver circuit.

2 ultrasonic receiver circuit

Composed of ultrasonic receiver and IC4 ultrasonic signal detection and amplification. Ultrasonic signals reflected by the 2-stage amplifier IC4 1000 times (60dB), 100 times magnification level 1 (40dB), 10 times zoom level 2 (20dB). Op amp needs due to the general positive and negative symmetrical power, and the device is used in single power supply (9V) power supply, to ensure its reliable operation, where R10 and R11 with the partial pressure, this time in the IC4-phase terminal the midpoint voltage of 4.5V, it can guarantee the quality of the amplified AC signal, and will not generate signal distortion.

C9, D1, D2, C10 double voltage detection circuit consisting of removing the detection of the reflected pulse signal sent to the IC5 processing.
IC5, IC6, IC7, IC8, IC9 composition of signal comparison, measurement, counting and display circuit, the comparison and measurement of pulses from the issue of detection and the pulse is reflected back to the time difference. It is the core of ultrasonic distance measurement circuit, the following analysis of their work.

By the Ra, Rb, IC5 component signal comparator. Which
Vrf = (Rb x Vcc) / (Ra + Rb) = (47KΩ x 9V) / (1MΩ + 47KΩ) = 0.4V
So when the A point (IC5 inverting side) over the pulse signal when the voltage higher than 0.4V, B point to the low voltage will be high 1 0. Noting that the same phase in the IC5 has capacitor C11 and diode termination D3, which is used to detect and prevent accidental setting. In actual measurement, the DME will be part of the issue around the ultrasonic receiver directly into the formation of false detection. To prevent this from happening, here D3 directly into an appropriate increase in IC5 test pulse to the comparator threshold voltage converter and the voltage from the C11 for a period of time, so the issue of detection of ultrasonic pulse transmitter, due to the role of the IC5 D3 conversion threshold voltage also will be raised, and because of the discharge to maintain the role of C11, when the test pulse to prevent interference with the formation of its own error detection. From the above we can see, when measured from the small to a certain extent, due to the anti-D3 and C11 error detection function, its close-measurement will be affected. Icon parameters around the minimum measuring distance of 40cm. Reduce the capacity of C11 in ambient temperature of 20 when the shortest distance be measured 30cm. At this point the discharge time is 1.75ms.