All of a sudden my DRSSTC Tesla coil stopped working.

It took a long exposure in a darkened room to see the very faint corona around the top of the primary coil – that’s definitely not right.

Ooh that's not good

The coupling between the secondary and primary coils was too tight. So I rewrapped the primary coil tighter and lower than it was before, and that seemed to fix things.

Not sure why that suddenly started to happen, as it’s been working great for about a year.

I recently came across a bunch of 4093 chips:

The NAND chip - 4093

These are Quad NAND gates, with Schmitt trigger inputs. It turns out you can use these to make oscillators and monostables – just like the 555, but more compact with less parts.

Astable oscillator with a NAND gate

So I updated the oscillator application I wrote to calculate out values using this oscillator as well as a 555. It looks like you can get more of usable range with this device.

Now with support for the 4093 chip

One thing – the NAND gates cannot source as much current as the 555 timers so you might need to add an opamp as a voltage follower. LM324 does this nicely.

You can download the C# solution here.

One nice feature of the 555 oscillator is that you can connect another LFO signal to pin 5 and create a vibrato effect for even more ‘musicality’ – something lacking with the NAND gates.

X rated - Cor!

I just watched The Long Good Friday – I’d forgotten about the X classification.

That means it’s really, really good.

Or something…