Measurement time 0.8 seconds. The sensitivity of the inputs is 0.3 V, with an input resistance of 13 kOhm.
A feature of the device is the ability to supply signals to three inputs, and, depending on the position of the toggle switches, the device will indicate the sum or difference of frequencies, thus - Y = f1 + f2 + f3 or Y = f1 + 2-f3 or Y = fl-f2- f3 or Y = f1-f2 + f3. The inputs on the front panel are arranged in a row, between them toggle switches are installed, the position of the lever of which - up means the action "+", down "-". In this way, you can set the lower mode of action with inputs.
The device has a seven-digit display scale and operates without switching limits in the entire range of measured frequencies.
The schematic diagram of the input device is shown in Figure 1- It contains three input amplifier-shapers on transistors VT1 - VT6. The input of each driver is connected to the corresponding input connector, designated - In 1, In 2 and In 3. The inputs are switched using three key devices, performed on the elements D1.1, D1.2 and D1.3 and the combiner D2.
Control signals from the control board are sent to the input board pins 8, 9 and 10 (Fig. 4). At any moment of the Burden of Measurement on one of these pins there is a stake, on the other units. The signal passes only the element whose input is zero. If one is given, this input is blocked.
Fig. 2
From the D2 output, the on-input signal is fed to the counting direction determination circuit. The counter and indication board (Fig. 2) has two inputs "+1" and "-1". When a signal is applied to its output 2, the signal goes to input 1 and the counter readings increase with each pulse, to output 3 - to input -1 and the readings decrease, the number of pulses is subtracted from the number of pulses already measured at the previous input.
To switch these inputs on the moisture inputs (Fig. 1), the D3 microcircuit is used. The control takes place from pin 11 of the board. When a unit arrives at this output, the D3.1 element opens and the pulses are fed to the subtraction input. When a zero is applied, this element closes and D1.2 opens, the pulses pass to the addition input. The signal to control the counting direction comes from the control board (Fig. 4).
Figure 2 shows a diagram of the counter and indication board. Directly, the counting of pulses is made by a seven-bit decimal counter on microcircuits D4 - D10. This counter consists of seven decimal counters with reverse, on K555IE6 microcircuits. They are included in sequence. After each measurement cycle, a decimal code is set at the counter output, which is numerically equal to the measurement result.
This code is obtained in this way, for example, three signals are added to the inputs - at 1n1 - 1000 kHz, at 1n2 - 400 kHz, at 1n3 - 200 kHz. Use the toggle switches to set the action - 1n1 + 1n2 - 1n3. The control board generates three measuring pulses of equal duration.
During the first pulse, the first input is opened and the number 100000 is written to the counter, the second input is turned on and the number 400 kHz is added (counted) to this number, it turns out 140000, then the third input is turned on and now the pulses are fed to the input -1 of the counter, the written number decreases at 200 kHz. It turns out 120000x10Hz = 1200000Hz.
If no signals are received at one or two inputs, then operations are performed with those to which they are received. For unconnected inputs, the number "0" is subtracted or added and does not affect the readings.
Settled at the output of the counter, after three cycles of measurement, the code is written into registers on microcircuits D11 - D17. It is more reasonable to use registers of the K555IR1 type here, but the author had only K555IE6 counters. These counters have preset inputs. When a zero is applied to pins 11 of these microcircuits, the code fed to their inputs 1, 2, 4, 8 is transferred to memory and appears at the corresponding outputs.
It is stored like this until the next negative pulse at pin 11. The counting functions are not used in this case. Thus, the code from the outputs of the counters is written into the registers, from the outputs of which it is fed to the decoders on the D18 - D24 microcircuits and then from their outputs the seven-segment code is fed to the LED indicators H1-H7.
Then the counter is reset to zero with a negative pulse from the control board to the terminals 14 of the counter microcircuits, and the cycle repeats. Again three measurements and then a write pulse arriving at pin 1 of the counter and indication board erases the information recorded on the D11 - D17 microcircuits in the previous cycle and the code of this cycle is written. The readings of the indicators change accordingly.
Fig. 3
Thus, during the zeroing of the counter and three measurements, the indicators show the result of the last completed cycle, that is, the previous measurement. As a result, there is no blinking of the indicator, just its readings change with a period of 0.8 seconds.
For the operation of any frequency meter, a reference frequency generator is required, equal to the minimum of the measured value. In this case, 10 Hz. The circuit of the driver board of this frequency is shown in Figure 3.
A signal of a stable frequency of 100 kHz is generated by a generator on a D25 microcircuit and a VT7 transistor. The frequency is stabilized by a quartz resonator Q1. In order to get 10 Hz, you need to divide 100 kHz by 10,000. For this, a four-link divider is used on the d26 - d29 microcircuits, all the same K555IE6 counters are used. From pin 7 of this board, pulses with a frequency of 10 Hz are fed to the control board.
Fig. 4
The schematic diagram of the control board is shown in Figure 4. It contains the D30 counter and the D31 decoder, which divide the measurement period of the frequency meter indication into eight sections. In the initial position at the D30 output, the number "0" and the zero level appears at pin 1 of the decoder, at the other pins at this time, units.
This zero through pin 4 of the board goes to the counters and indication board and sets its counters to zero position. Then, with the arrival of the first pulse, zero appears at the second pin D31 and through the VD7 diode it is fed to pin 11 of the input board and turns on a positive count. Then the next impulse turns on the first input. This is followed by an impulse to set the counting direction again.
In this case, the S1 toggle switch stands in the way of this impulse. In the closed state, zero is supplied to pin 11 of the board; in the open state, it is one, and the counting direction changes accordingly. The next impulse turns on the second input, then again the presetting of the direction, in this case the S2 toggle switch is involved, and now the third input is turned on.
When the eighth pulse arrives, a negative drop at pin 1 of the board turns on the recording of information into the D11-D17 microcircuits of the counter and display board (Fig. 2).
Then the cycle repeats again. The device is powered by a stabilized power supply, the circuit of which is shown in Figure 5.
Fig. 5
All parts are mounted on four printed circuit boards, wiring and wiring diagrams are shown in the figures in full size. The power supply is mounted in bulk, the A1 chip must be placed on the heatsink. You can use a source made up to a different circuit, it is important a stable voltage of 5V and a current of up to 1A.
Power transformer T1 is wound on the core ШЛ20х25. The mains winding contains 1000 turns of wire PEV-2 0.2. secondary winding - 65 turns of PEV-2 0.68. As D11 - D17 microcircuits, you can use K555IR1, K155IR1, when changing the board layout, or K555 (155) IE7 without changes. If you use gas-discharge indicators, you can replace the K514ITs2 decoders with K155IL1, change the board drawing.
With a change in the wiring, instead of D26-D26, you can use K155IE2 or K555IE2 meters, D30 can also be replaced with K155IE2. All diodes can be KD521 or KD522.
If the device is used as a separate device, its boards are located in a metal case with dimensions of 220x300x80 mm, a ready-made case is used, produced specifically for amateur radio construction. By making the case yourself, the frequency meter can be made more compact.
Simple charger for a car battery
In old TVs, which still worked on lamps and not on microchips, there are power transformers TS-180-2
The article shows how to make a simple transformer from such a transformer. DIY battery charger
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Device diagram:
Have TS-180-2 there are two secondary windings, designed for a voltage of 6.4 V and a current of 4.7 A, if they are connected in series, we get an output voltage of 12.8 V. This voltage is enough to charge the battery. On the transformer, you need to connect pins 9 and 9 with a thick wire, and a diode bridge, consisting of four diodes D242A or others rated for a current of at least 10 A.
Diodes need to be installed on large radiators. The structure of the diode bridge can be assembled on a fiberglass plate of a suitable size. The primary windings of the transformer must also be connected in series, a jumper must be placed between terminals 1 and 1 stroke, and a cord with a plug for a 220 V network must be soldered to terminals 2 and 2. It is advisable to install fuses in the primary and secondary circuits, 0.5 A in the primary circuit, secondary 10 A.
The wires that you use in the manufacture of the charger must have a cross section of at least 2.5 mm2. Radiator area for a diode, not less than 32 cm2 (for each). In our case, the secondary windings are designed for a current of 4.7 A, therefore it is impossible so that the charging current exceeds this value for a long time. The voltage at the battery terminals during charging should not exceed 14.5 V, especially if a maintenance-free battery is being charged.
In our device, the charging current is limited due to the small output voltage of the transformer (12.8 V), but the value of the output voltage depends on the value of the input. If your network voltage is more than 220 V, then, accordingly, the output of the transformer will be more than 12.8 V.
You can limit the charging current by connecting a 12 volt lamp with a power of 21 to 60 watts in series with the battery in the gap of the negative wire. The lower the lamp power, the lower the charging current will be. To control the current and voltage, it is necessary to connect to the charger an ammeter with a measurement limit of at least 10 A, and a voltmeter with a measurement limit of at least 15 V. Or you can buy a multimeter with a current measurement limit of at least 10 A and periodically monitor the parameters with it.
Connect the battery carefully. It is not allowed even for a short time to confuse plus and minus when connecting the battery. Also, it is impossible to check the operability of the device by short-term short-circuiting of the terminals ("spark test"). The charger must be de-energized during connection and disconnection of the battery. When making and using the charger, be careful, follow the rules of fire and electrical safety. Do not leave the operating device unattended.
See the diagram of another charger for
