Improved Impulse Detector with CD4029N

An impulse detector circuit observes input pulses from an external sensor/source and converts into a processable output signal. Described here is a microcontroller-compatible event detector circuit built around one long-familiar CMOS presettable up/down counter chip, CD4029N from Intersil.

Circuit Description

Here, the presettable up/down counter CD4029 (IC1) is configured as upward counting decade counter, resets to zero in a pre-defined routine impelled by an external reset pulse generator. Pulses, for observation, are routed to the clock input of CD4029 through a BC547B (T1) transistor. Green LED (LED1) in the circuit works as “standby” indicator, and the Red LED (LED2) functions as “attention” indicator. Note that, flashes from the Red LED represent a multi-fold increase in events over the Green LED. Events are counted in fixed periods, determined by the external reset pulse generator circuitry. The whole circuit can be connected to any 5V/3.3V dc power supply rails.

impulse detector circuit diagram

(impulse detector circuit diagram)

Application Example

As stated, this improved impulse detector receives input pulses from an(y) electronic sensor and watch them to produce an alert when necessary. The circuit needs an external time base – the reset pulse generator – for the alert generation task. It is possible to supply the reset pulses from a vacant I/O port of an existing microcontroller (this calls for a few lines of additional code), or from a square wave generator circuit built around discrete components.

Presume that you are building a microcontroller-based spark sensor system using one dedicated spark sensor module as the front-end, and the spark sensor module outputs 8 iterated pulses (per half-second) in case of an unfeigned spark detection. In this circumstance, a 500ms reset pulse should be required for the impulse detector to raise an alert by switching its “attention” LED. Here, flashes from the “attention” LED (red) represent an eight-fold increase in events over the “standby” LED (green). Since the counter reset to zero twice a second, events are counted in 500ms periods. The system diagram shown below may be easier to interpret than the blurring maths.

impulse detector application example

(application example – system diagram)

Construction & Testing

Due to small number of components used, it’s unlikely that the construction of the circuit will give you sleepless nights. The use of a small veroboard makes things easier,see the author’s prototype. Carefully check the finished circuit board before applying power, and try to mount the assembled circuit in a small plastic base with a double-sided glue-tape stuck on the bottom. Once power supply has been switched on and the reset pulse input have been connected, the impulse detector is ready for use. But first the reset pulse input needs to be adjusted as per the real requirements.

Since absolute reset pulse waveform will not available very often, the impulse detector could be calibrated more practically. All you need for this is a 500ms square wave generator (555 or 4001 IC-based), output of which is connected to the RST_IN (J2) of the impulse detector. Now ensure that the “standby” indicator (LED1) is active, and the “attention” indicator (LED2) lights up when an 8 pulse/500ms input is appeared at the PULSE_IN (J1) of the impulse detector. Again, use another square wave generator for suitable pulse generation to perform this task.

author’s prototype

(author’s prototype – under testing)

oscillogram of the reset pulse used for testing

(oscillogram of the reset pulse used for testing)

After the previous description it should be clear how the impulse detector should be used in real-world applications. The reset pulse (flowed to J2) should always be kept in the exact “frame” according to the pulse-rate output of the implicated sensor (connected to J1). An acoustic sounder or relay can be connected in lieu of the “attention” indicator, or you can use the output available at the test point (TP1) for further processing by your favorite microcontroller. And that’s it!