vacuum tube to pic -- how?

[tiny2]

I've been working on a little novelty project to combine the two types of technology. Just wondered if anyone had any safe suggestions on how to interface the crystal oscillator to a pic CLKIN pin.

Here's what I have so far. The oscillator circuit was borrowed from an old shortwave receiver. The main difference between the circuit below and the actual prototype is the inclusion of a 1.5k resistor in the cathode. The tube used is the nearest equivalent I could find.

A picture of the prototype built on an old scrap chassis.

Here is the signal available at the anode. With approximately 130V applied, the measured current is around 1mA.

Across the cathode resistor is shown below, maybe I could fit a buffer transistor in there somehow ?

Any suggestions welcomed.

regards..

 

[stevez]

Keep in mind that a short in C36 will make plate voltage available past that point. I know you might do something differently - just calling it to your attention.

 

[Nigel Goodwin]

Feed the output from C36 into a high input impedance buffer, probably via an attenuator - then clamp the output to 0-5V to feed the PIC.

 

[ljcox]

Another way to do it would be to wind a transformer and insert it in the anode circuit in lieu of the resistor. However, you will need the correct resistor in the cathode circuit in order to set the anode current.

The transformer could be wound on a ferrite ring. This would be the safest option for the PIC since there will be complete isolation between the primary and secondary PROVIDED THAT you don't wind the secondary directly over the primary.

 

[Rolf]

750 Ohm ......

Across the cathode resistor is shown below, maybe I could fit a buffer transistor in there somehow ?

Any suggestions welcomed.

regards..

Why not drop the cathode resistor to 750 ohms and put a 5v zener diode across it for safety? This would clamp the signal to a safe level for the PIC. For additionally safety you could use capasitive coupling.

 

[Hardwire]

I would use a high speed optocoupler like this one:

http://www.sensitron.com/data_sheets/4134.pdf

Best to leave the vacuum tube technology in one world, and the PIC in another (IMO). You won't even have to reference them to the same GND.

 

[Nigel Goodwin]

Best to leave the vacuum tube technology in one world, and the PIC in another (IMO).

Best not to even consider such an incredibly stupid and pointless exercise!

 

[kchriste]

Best not to even consider such an incredibly stupid and pointless exercise!

Now if only the OP had decided to drive a tube amp with PWM from the PIC for a richer higher distortion sounding BEEP.....

 

[Hardwire]

Best not to even consider such an incredibly stupid and pointless exercise!

I do suppose I was taking the less challenging route

 

[tiny2]

Thanks all for replies. Not forgetting that this is just a novelty project; not to be taken too seriously !!

I thought that the optocoupler was a good idea, although I don't happen to have any here of adequate sensitivity to try. So I'll go with reducing the cathode resistor to give me the appropriate voltage. I had originally intended to use a miniature wire-ended pentode instead of the EF95, so maybe I'll implement that change first.

Thanks and regards