PCB assembly discussion

[Tony]

This is the first of a new batch and I'll update the instructions shortly. 333 is 33n, brown black red is 1k used in place of the 1k2. The relay triggering was too sensitive so the 3k3, which usually required a 5k6 across it, reduced to 2k2. I can send another elay with the USB socket. What is the voltage at pin 3 of IC1 and did you remove the solder bridge across C6?.

[jmmcg]

This is the first of a new batch and I'll update the instructions shortly. 333 is 33n, brown black red is 1k used in place of the 1k2. The relay triggering was too sensitive so the 3k3, which usually required a 5k6 across it, reduced to 2k2. I can send another elay with the USB socket. What is the voltage at pin 3 of IC1 and did you remove the solder bridge across C6?.

The bridge was already removed, before I reported these issues, checked for other solder bridges. Checked component orientation. I cannot find a fault. Voltage at pin 3 of IC1 is ~2.11V if the NIXIE is not "stimulated", raising to ~2.34V or a bit higher if I put two fingers on the NIXIE (pretty difficult trying to hold the probes & touch the NIXIE...).

N.B. The nixie glows nicely & responds to touching with a change of glow.

[Tony]

What is the current draw? that voltage is a little low.

[jmmcg]

What is the current draw? that voltage is a little low.

I tried measuring it again today and got totally different readings (hhmmmm - me or AVO meter? probably both . I now seem to get about 9V without stimulating the nixie (bit high, but may not trigger the relay) and 20V when stimulated; this looks o.k.-ish to me - it might trigger a relay (not the one I managed to kill though...). I'm happy to pay for the replacement & p&p, please let me know via email.

[jmmcg]

What is the current draw? that voltage is a little low.

I tried measuring it again today and got totally different readings (hhmmmm - me or AVO meter? probably both . I now seem to get about 9V without stimulating the nixie (bit high, but may not trigger the relay) and 20V when stimulated; this looks o.k.-ish to me - it might trigger a relay (not the one I managed to kill though...). I'm happy to pay for the replacement & p&p, please let me know via email.

I measured the voltages to to the driver for the relay coil: 1st attempt ~6.5V increasing to 21V, 2nd: 5.5V increasing to 21V
Pin 3 measures 2.2V at all times.
Pin 2 4.8V

[jmmcg]

Might having an earth strap around the nixie have an impact upon if the relay works? Could it overstimulate the nixie? This would cause the relay to be fired at start-up, yet the capacitor would never get charged, so the relay may not actually fire ever.

[Tony]

Yes it can, experimenting with the resistor value to increase or reduce the trigger voltage is required due to the handwound coil and other variations.

[jmmcg]

Yes it can, experimenting with the resistor value to increase or reduce the trigger voltage is required due to the handwound coil and other variations.

Have you any suggestions regarding values I should try replacing it with (or would a 1k-10k potentiometer cover the necessary range)? And just to be clear, specifically which resistor (I presume we are referring to R4)?

[Tony]

A 10k variable would do but there's usually quite a large voltage change anyway meaning there's a wide acceptable range.

[jmmcg]

A 10k variable would do but there's usually quite a large voltage change anyway meaning there's a wide acceptable range.

I have added a 10k trim potentiometer in place of R4 to two of the Buttons of Doooom: both have 27 turns (I did my level best to follow your advice and make the coils even & tight) and swapping the nixie (*), with the pot adjusted to about 4.5k, the relay reliably fires when the nixie is grasped (**). Note that I omitted the optional earth strap to simplify matters for me (***).

I am experimenting with the other Buttons of Dooom and will edit this post to add the details for them.

A result of this experimentation is that I strongly urge that the fixed R4 is replaced with a 10k trim potentiometer in future kits. (Without this trim pot, I have never managed to get the three Buttons of Doooom built so far to fire the relay at all, with it I have managed to get two working so far.)

(*) All of the nixies seem to work, but some seem more sensitive than others: I swapped to one that did not "avalanche" until touched. (Follow Tony's advice! Leave sufficient tails to the coil so that extra turns may be added/removed to ensure that the nixie only glows when touched. I failed to do this for the two I am testing, hence swapping.)

(**) I need to almost completely enclose the glass envelope of the nixie in my hand, even enclosing a portion of the brown base to cause reliable triggering. For me the capacitor that fires the relay takes a reliable 20sec to have sufficient energy to fire the relay.

(***) With an earth-strap: this could be a major pain: to avoid tearing your hair out (with an earth strap 3 hours and counting trying to adjust the pot, yes that bad): glue it to one of the adjacent holes (I did not do this - big mistake!), so that it may be adjusted once the button is assembled with the washers & bolts attached. This is MOST tedious, as even the housing and ... tightening the bolts affects the triggering resistance! The pot must be adjusted AFTER complete assembly (including any varnishing)! Even putting it on a conductive surface affects the triggering resistance (and can cause spontaneous triggering)!!! By gluing the pot to one of the holes, with the strap, assembled, it took less than 10 mins to get the relay working. The resistance is just over about 7k.