VCO on the K0308018 chip. Scheme, description

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VCO on chip K0308018. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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An old unnecessary Genius two-button ball computer mouse model CG1402002889 had a circuit board with a controller on the K0308018 chip installed. Unfortunately, no useful information about this microcircuit was found on the Internet, so simple experiments were carried out to find out if there was any possibility of using this microcircuit for another purpose.

A voltage of 5 V was applied to the computer mouse board from a laboratory power supply. Using an oscilloscope, a rectangular signal with an amplitude of about 5 V and a frequency of 5 kHz was detected at pin 66 of this microcircuit. It was found that the frequency of the signal at this pin depends on the voltage at pin 16, which was set using a 270 kOhm resistor installed between this pin and the positive power line. As a result of the experiments, a voltage-controlled generator (VCO) circuit appeared, the output frequency of which can be changed a million times with one variable resistor without switching ranges.

The device diagram is shown in Fig. 1. The generator frequency is set with variable resistor R1. The higher the voltage at pin 16 of the DD1 chip, the higher the frequency of the output signal. At a voltage of 0,54 V - frequency 10 Hz, at 0,74 V - 1000 Hz, at 0,87 V - 10 kHz, at 1,06 V - 50 kHz, at 1,2 V - 100 kHz. The signal shape is a rectangular meander. In the latter case, reducing the supply voltage from 5 to 3,3 V leads to a decrease in frequency from 100 to 72 kHz. With the variable resistor R1 in the upper position in the diagram, the minimum voltage of the device at which it remains operational is 0,9 V, while the output signal frequency is 31 Hz. With a supply voltage of 5 V, a frequency of 100 kHz and no load, the current consumption is 12 mA. At a frequency of 0,1 Hz, the generator consumes a current of 3...7 mA. With an increase in the temperature of the microcircuit case to 80^оThe output frequency of the generator increases by 1...2%.

VCO on the K0308018 chip
Rice. 1. Diagram of the device

The generator output (pin 5 of DD1) is relatively high-resistance, so the signal to the load is supplied through a buffer push-pull amplifier assembled on transistors VT1, VT2. An indicator on a two-crystal two-color LED HL1 is connected to the output of the amplifier, which glows green when the output voltage is low, and red when the output voltage is high. The flickering of the LED is noticeable at a frequency of up to 30 Hz, after which the color of the glow becomes yellow-orange. Resistors R11, R12 limit the current through the LED.

Diode VD1, together with fuse link FU1, protects the device from power supply voltage reversal, which can occur when the structure is operated from a laboratory power supply during its setup.

Capacitors C1, C2, C4 are blocking capacitors in the power supply circuits. Capacitor C3 suppresses noise and interference at the control input of the DD1 chip.

In addition to the variable resistor, LED and fuse link, all parts of the generator are installed on a circuit board measuring 26x50 mm (Fig. 2). The board from a disassembled mouse was used. Unnecessary protrusions on the board have been cut off. Unnecessary parts and tracks have been removed. New connections are made with thin installation wires; the remaining printed conductors are used for some of the connections. Some elements are installed on the wiring side.

VCO on the K0308018 chip
Rice. 2. Parts on the circuit board

Fixed resistors P2-23 or imported ones are used, variable resistors - SP3-9a, SP4-1. To smoothly adjust the frequency in series with resistor R2, you can install a variable resistor with a resistance of 1...4,7 kOhm in a rheostat connection. Capacitor C1 is a small-sized imported oxide capacitor, the rest are film or ceramic, for example, K10-17, K10-50. The KD208A diode can be replaced by any of the KD209, KD212, KD243, KD247, Sh400x, FR15x series. Replacement of the KT3107D transistor - any of the KT3107, KT6112, KT6115, KT668, KT684, 2SA910, SS9012 series. The KT3102IM transistor can be replaced with any of the KT3102, KT6111, KT6114, KT645, KT660, KT683, 2SC1815, SS9013 series. The L-937EGW LED with red and green crystal glow colors can be replaced with any similar one, preferably with increased light output, for example L-57EGW.

Depending on the specific requirements for the output of the device, instead of an amplifier on transistors VT1, VT2, you can connect, for example, the input of a CMOS or TTL microcircuit. It is not necessary to supply voltage to the control input of the DD1 microcircuit from the resistive voltage divider shown in the diagram. The source of the control voltage can be any sensor of a non-electrical quantity, for example, a light, humidity, temperature sensor, but the control voltage should not be greater than the supply voltage of the device. When the supply voltage is 5 V and the control voltage is more than 3,2 V, generation stops. With a control voltage of 2,9 V, the output pulse frequency is about 2,6 MHz, and the current consumption is 55 mA. Since the parameters of the K0308018 chip were unknown, this operating mode was tested briefly.

Author: A. Butov

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