Simplified ultrasonic gasoline octane number meter. Encyclopedia of radio electronics and electrical engineering

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To compare the propagation delay of ultrasound in the tested gasoline with the reference ones for its four grades (see the article "Ultrasonic octane number meter for gasoline"), a digital comparator was used in it. It turned out that this entire assembly (a digital comparator with buffer elements - six microcircuits) can be replaced with one microcircuit of a programmable read-only memory (PROM), which greatly simplifies the device.

Since the distance between the receiver and the ultrasonic emitter does not exceed 2 m, high sensitivity of the ultrasonic receiver is not required. Therefore, it was possible to replace its input amplifier on an op-amp with a cheaper and simpler amplifier on a single transistor.

A diagram of a simplified ultrasonic gasoline octane number meter is shown in fig. 1. The algorithm of the device has not changed and is described in detail in the previous article. Only now the code from the outputs of the counter DD3, corresponding to the measured propagation delay of the ultrasonic pulse in gasoline, is not sent to the comparator, but to the address inputs of the PROM Ds1 (KR556RT4A).

Rice. 1. Diagram of a simplified ultrasonic gasoline octane meter (click to enlarge)

Chips of this type are supplied to consumers with logical zeros recorded in all memory cells. To use the PROM in the device, it must be programmed by replacing the logical zeros with logical ones in the required cells. The addresses of the PROM cells and the codes that need to be written to them are shown in the table. In all other cells that are not in the table, the code 1111 should be written.

With the PROM programmed in this way, the HL1 LED of the device will turn on when checking AI-80, HL2 - AI92, HL3 - AI95 gasoline. Gasoline with a higher octane rating than AI-95 corresponds to the glow of the HL4 LED, and if gasoline is worse than AI-80, all LEDs will be turned on.

Setting up the device comes down to setting the frequency to 40 kHz at the output of the DA1 chip generator (pin 5) using the trimmer resistor R7 and programming the PROM. You can program the KR556RT4A chip manually using a programmer, the circuit of which is shown in Fig. 2. Program it by applying single programming pulses to the output of the programmable discharge and to the power output. The cell address is dialed with the SA1 and SA2 coding switches, the bit to be programmed is selected with the SA3 switch. The pulse burns out the fusible jumper inside the microcircuit, which is equivalent to writing a logical unit to this bit.

Rice. 2. Diagram of the programmer

When you press the SB1 button, a single pulse generator on a single vibrator DD1.1 produces a pulse with a duration of about 100 ms, which opens the key on transistors VT1 and VT2. During the pulse, +12 V is supplied to the programmable discharge and the power output of the PROM. If the unit is written, the HL1 LED should turn on. Otherwise, the write operation should be repeated. The duration of the programming pulse depends on the values ​​of the resistor R10 and capacitor C1.

The KR556RT4A chip has long been discontinued, but there are still quite a few of them on sale. If necessary, you can use other PROM chips, for example, K155RT4, K541RT1 or imported ones.

Author: A. Kornev

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