Testing the TK Tar Baby

[picowatt]

TK,

Regarding the alternate bias using the first batt tap (+12v), you will have to either remove Q1 or tie its gate to it's source and Q2's gate will have to be isolated from the rest of the circuit.  I.e., pull Q1 out and then hook up the 12V via 100K or better to the Q2 gate.  The 50R can go across the current FG terminals (between Q2 source and the CSR).  That should give you similar DC bias conditions for Q2, but as I said, at AC things get a bit muddied.

Do you have a rough idea as to the frequency of the osc?  I am not so sure the LED's in the video were lighting due to AC current through the CSR in the "traditional" sense.  Assuming 1.4V turn on for the LED's, that would require about 5.4 amps going thru the CSR, yet you say the load barely warms during the osc.

What happens to the LED's if you touch them with your fingers while the circuit is oscillating?

Have you looked at the CSR with a scope channel during the osc?  Does it give you any clues as to the actual voltage/current happening there?

PW






     

[TinselKoala]

Tar Baby and the Semi-Deluxe LEDs of Doom:
http://www.youtube.com/watch?v=MEmNZtt3zZ8

[picowatt]

TK,

Congratulations, your green LED, after 92 seconds of electron loading into its crystal lattice, has finally acheived a Can't OPerate factor (COP) of infinity.

PW

[MileHigh]

TK:

Thanks to you and Mags on the reminder about the typical current through a vanilla LED.  It's been a long time for me.  The last time I wired up a vanilla LED like that was probably 30 years ago.  Yikes!

Realistically, a 20 or 30 mA LED may be able to withstand 100 mA.  The trick is to check how hot they are getting with your finger and thumb.

Okay I have a Rev 2 for you.  For starters I meant two LEDs in parallel back-to-back with two LEDs in parallel.  That might still be pushing it so if you have a small breadboard handy, if you did 4 LEDs in parallel back to back with 4 LEDs in parallel you will probably be fine.  No series resistor!

MileHigh

P.S.:  I remember putting 5 volts through a vanilla LED with no series resistor.  It made a cracking sound like a firecracker and split in two after about five seconds.  Not as much fun as over-voltageing a small DC motor hanging by it's wires and hearing it scream and spin itself into a spiral of death.  Screw them people for the ethical treatment of motors.

[MileHigh]

PW:

Do you have a rough idea as to the frequency of the osc?  I am not so sure the LED's in the video were lighting due to AC current through the CSR in the "traditional" sense.  Assuming 1.4V turn on for the LED's, that would require about 5.4 amps going thru the CSR, yet you say the load barely warms during the osc.

You are really good and I am losing my touch/getting lazy.  Would it be due to an effective capacitance associated with the PN junctions?  I think the frequency is in the low megaherttz range but TK will confirm.

MileHigh

P.S.:  TK, just watched the latest clip.  I would think that you are in the MHz range because of both LEDs partially lighting when you shorted them out.  That's a pain in the butt in a way, that very high frequency.  It complicates everything and puts things in "magical Dr. Stiffler" territory.  I was thinking the other day about the sampling rate issues for the DSO and all that, something that Poynt and I touched on last year.  Running at high frequencies like that makes things that much more complicated and certainly way out of the realm of competence of the RAT team.  Now the placement of the wires is that much more critical and so on.  However, it should still not throw off the Rev 2 Deluxe LEDs of Doom test.