High Precision Digital Pulse Meter Circuit

This small device, intended primarily for modellers, allows an instant reading of the time I of a pulse in ms. It can, for example, measure the position of the servomotors, about 1 to about 2 ms, or make repetitive or non-pulsed measurements, such as closing or opening times of any instrument, parasitic abnormality. The diagram just describes the operation of this device. The pulse to be measured is displayed at the input of the inverter IC1 / 1 trigger gate. This gateway allows a slight reset of the signal format and displays an input impedance high enough to not disturb the signal. The output of the IC1 / 1 disables the counters 4017 and 4520 (IC2 and half IC3).
High Precision Digital Pulse Meter Circuit - schematic

High Precision Digital Pulse Meter Circuit - img1

High Precision Digital Pulse Meter Circuit - img2

High Precision Digital Pulse Meter Circuit - img3


• Measurement range between 0.01ms and 9.99ms with a resolution of 10μs
• Visual self-testing of indicators during activation.
• Underestimation of scale (> 9.99mS)
• Memory function for instantaneous pulses
• 9V battery supply
• Power consumption approx. 110mA to 130mA

The Main Operation of the Circuit

If a conventional 4MHz crystal is selected and corresponds to a 0.25 ms period, we will have to multiply by 40. The integrated IC2 is a decimal counter that will perform the multiplication by 10 and half IC3 (double binary counter ) Will multiply by 4.

At exit, we will have the presence of 40x 2.5μs = 10μs. They are measured by circuit 4553 (IC4) at terminal 12 (CLK input). Given the 10μs resolution, for example, if there are 160 bits of 10μs, the input signal is 160x10μs, that is, 1600μs, so 1.6ms. Input of the input signal is generated Thanks to the R7 / C7 and the integrated IC1 / 2, a LE signal with a duration of about 30μs. This, which allows the triggering of 4553, which will send and, most importantly, block the result of enumeration in the indicators (memorization). The end of the LE pulse will in turn produce a RESET pulse at IC4 terminal 13 after one pass from IC1 / 3, R8 / C8 and IC1 / 4 to prepare it for the next measurement. This RESET pulse will reset the counter to zero but will change the display. As long as LE is always at + 5V, the data remains available at the output. They are multiplied at a determined velocity by capacitor C6 and decoded by IC5 (7-segment decoder, 4511).

Observe the R9 / C9 circuit at terminal 3, LT. Its components allow each moment the meter starts to apply a low-power mode momentarily to command the activation of all segments (auto-test with activation) and to verify that there is no problem. Transistors T1, T2, T3 control the cathode of each indicator without loading IC4 (4553). Resistor R6 shows the split point between ms and ms to get an instant read. Resistors R12 to R18 limit the current to the indicators to avoid any degradation.

We have the key features in this way. Instant reading in ms, 10μs resolution, memorization and self-test. We still have to study the depiction of exceeding the available scale. In fact, for reasons of simplicity, we preferred to use the second half of the binary counter 4520 (IC3) and remain free. The OF445 output of IC4 produces a positive "OF" pulse if the scale is exceeded (if the value is greater than 9.99 ms).

In normal mode, Q0b has the value "0", so the same thing happens with CLKb. It is therefore the frontal cavity of "OF", which will increase the value of the meter. Output Q0b will overcome status "1". Because of this, CLKb input is at "1" and blocks the counter.

Transistor T4 controls and scans the two AF1 and AF2 AF points by recording an excess of the available range. The counter must now be disengaged to overcome this overrun, which remains as a fixed indication. For this reason, the R10 / C10 loop is added slowly (since Q0b passes to "1") and sends a reset to zero at the RESET input after about one second. The two points are extinguished. The Q0b and CLKb are reset to "0" and the counter is ready for the case of a new overrun of the scale.

Important Note: Scaling is not memorized as it automatically turns off. The IC6 circuit allows the power supply to stabilize at + 5V. Capacitors C1 to C5 and C11 filter the parasites on the feed lines.

The Construction 

The printed circuit, which is single-sided, has dimensions of about 63 x 66mm. Figure 5 shows the mounting of the components on it. Glue first of all three bridges. The first, which is very small, is located just below the AF1 indicator. The second is under IC4 and the third left of IC2. Then paste the terminals of the integrated circuits. It is better to place the markers on bases to lift them as high as possible to fit them into the box. In this case, use a low profile crystal for QZ (about 4mm high) if necessary. Glue the resistors, capacitors and then the QZ crystal. Now stick the 5V stabilizer, the integrated IC6 and screw it onto the circuit for greater robustness and to get the maximum heat.


Feed the circuit (for example, with a 9V battery) at the "+" and "GND" points on the left of the IC6. Verify the presence of + 5V at the terminals of one of the filtering capacitors (C1 to C5 or C11). Disconnect the battery. Glue the transistors in the direction of their placement. Place the integrated circuits (caution in their turn) and all three indicators in their place. The signal input is at the 'INPUT' and 'GND' points from the left part of the R4 resistor.


Short the "INPUT" and "GND" and turn on the circuit, you should read 8.88 (self-test), then 0.00 (measured value). For use in modeling, you can build a small 3-pin fitting connector that allows the circuit to be inserted between the receiver and the servo drive.

You should therefore read values ​​between 1 and 2ms, depending on the position, without harassing the whole of the receiving device. It is, on the contrary, normal to observe a deviation of the servo drive when the counter is no longer being fed. This device proves extremely useful for setting up remote-controlled sets, in particular for adjusting pulse width modulated encoders.



R1-R3: 100Ω
R5, R6, R11: 100Ω
R4: 1MΩ
R7, R8, R9: 100K
10: 220KΩ
R12-R18: 47Ω
C1-C5, C11: 100nF
C6: 1nF
C7, C8: 470pF
C9, C10: 10μF / 16V
IC1: 4584, 40106
IC2: 4017
IC3: 4520
IC4: 4553
IC5: 4511
IC6: 7805
T1-T3: BC558
T4: BC237
AF1-AF3: Common Cathode 13mm TDSR5160
QZ1: crystal 4MHz HC49 / 4H


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