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CD40106 Hex Schmitt Inverter IC

One of my processes for choosing a topic or theme for this blog and video is to look into the "buckets of wire critters" and randomly choose an IC, then research for a bit about how it might be usefully employed.

And so it came to pass that I spied a few CD40106 ICs which I had ordered in June of 2018 (and then forgotten).

The CD40106 is a hex Schmitt-Trigger inverter which has a score of useful circuits with it at the heart. For instance in the datasheet we see applications including wave and pulse shapers, high-noise-environment systems, monostable multivibrators and astable multivibrators.

Here is the pinout:

However, in the course of researching I found a "train crossing" circuit which used three 555 chips to simulate a warning and then actual flashing LEDs.

I was surprised that this 555 based circuit came up as a "hit" when I was searching for CD40106 - but when checking the bottom of the website I found the following circuit.

Whilst the circuit is fairly simple to both understand and construct, I was stymied by the first lot of ICs I picked up being clearly faulty.

Firstly, they did not behave as expected (blinking at odd times although not as per the circuit). The biggest problem was that after a few minutes they went into a short circuit, thus triggering the current limiter on my power supply, and refusing to do any more work!

Fortunately the second batch I tried worked and worked well.

I'm thinking that although this was a "train crossing" application it would suit an "alarm" style circuit - perhaps even with a "cancel" option as per a commercial home alarm.