IR locator for the blind. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electronics in medicine
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Relatively small in size, the infrared (IR) locator warns with a sound signal about approaching some kind of obstacle (wall, fence) or object. The signal appears at a distance of about 1,5 m from the obstacle, and as it approaches further, the signal frequency gradually increases.
The diagram of the locator is shown in fig. one.
(click to enlarge)
An IR receiver and an amplifier are assembled on the VD1 LED and the DA1 chip, a controlled audio frequency generator on the VT2 transistor, and an IR transmitter on the VT3, VT4 transistors and HL1 ... HL3 LEDs.
Consideration of the work of the locator will begin with the transmitter. On the transistor VT3, a generator of short pulses is assembled, following at a frequency of about 1000 Hz. After charging the capacitor C7 to a voltage of 5 ... 6 V, it is quickly discharged through the transistor VT3 and the emitter junction of the transistor VT4. In this case, the transistor VT4 opens, and a current pulse flows through it and the LEDs, as a result of which an IR radiation pulse appears.
The IR pulse reflected from the object hits the receiving LED VD1 and is converted by it into an electrical signal, which is then fed to an amplifier assembled on an operational amplifier (op-amp) DA1. The amplified signal is fed to a rectifier made on diodes VD2, VD3 according to the voltage doubling (addition) scheme. The rectified signal is smoothed by the capacitor C5 and fed to the controlled AF generator. If the distance to the object is more than 1,5 m, then the power of the reflected IR radiation, and hence the voltage at the input of the controlled generator - the emitter of the transistor VT2, is not enough for its operation.
When the distance decreases, the level of the reflected signal increases, and the AF generator starts to work. Moreover, the larger the reflected signal, i.e. the closer the reflective object, the faster the capacitor C6 is charged and the higher the frequency of the generator. A small-sized BF1 headphone is used as a sound emitter. The threshold for the operation of the generator is regulated by a trimming resistor R4.
For a clearer operation of the generator and its stable operation, power is supplied to the generator through a parametric voltage regulator on the VT1 transistor and the VD4 zener diode. In general, the locator is powered by GB1 and GB2 batteries, each of which consists of four D-0,06 batteries connected in series. An external telephone can be connected to the locator via connector XS1, while the internal telephone is switched off.
For periodic recharging of the batteries, the locator has an XS2 connector, which includes a plug from the charger assembled according to the one shown in Fig. 2 scheme.
The HL1 LED in it signals the charging of the batteries. Capacitor C1 must be paper with a rated voltage of at least 400 V, and diodes - any rectifier with a maximum reverse voltage of at least 300 V.
When operating the locator, it should be remembered that it reacts to the infrared radiation of incandescent lighting lamps at a distance of several meters.
Author: I. Nechaev, Kursk
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