Need help with this photon torpedo circuit

MillenniumFalsehood · Post by **MillenniumFalsehood** » Sat Feb 18, 2012 3:23 am

Okay, I found a pretty good photon torpedo effect circuit online that seems to work in the video:

http://modelslouch.wordpress.com/2010/08/15/254/

So I copied the diagram, made a component list, then ordered the components and waited patiently for them to arrive.

Fast forward a few days and here I am trying to build this thing on a breadboard. I double-checked everything and made sure that I put it together right. Then I hooked up a 6v power supply, like it called for, and then . . . I ended up with a $27 flashlight. The LEDs light continuously, and nothing happens when I hit the pushbutton.

Now, I identified a few possible sources for the problem:

1) I have no idea what kind of diodes he used, so I picked a couple out of my parts bins. They are black, about 1/16" in diameter, and have a silver band on the end.

2) The capacitors I ordered may be too small and can't handle the amperage. They're 3w, 10uF capacitors.

3) A couple other capacitors are old ones from my parts bin that I desoldered from a broken TV's board, so they may be bad (they're the 47 and 220 uF capacitors).

I can take a picture of my setup, but hopefully someone here will know what's probably going on just from my description. I did check for short circuits, but there are none save for the one in my DVD player.

USS Atlantis · Post by **USS Atlantis** » Sat Feb 18, 2012 3:48 am

1) The diodes are probably 1N4148 signal diodes

2) Only place he's using a 10uf is across the power leads to level the spikes in the current - make sure that it's a polarized cap as well and that it's installed correctly - and a 3watt should be fine

The others (C2, C3, C5, C6) are 10nf - which is a smaller rating

3) Caps are pretty hard to destroy that way, I've got some here I got the same method and are 30+ years old

Way to check - get a multimeter that has a capacitor tester

Or rig up a simple blink circuit on a breadboard using the cap and a resistor

MillenniumFalsehood · Post by **MillenniumFalsehood** » Sat Feb 18, 2012 6:57 am

About the switching diodes: what are those exactly? Would they prevent the circuit from working properly?

So they're not 10uF; I misread them. What is 10nF? I've only seen ratings in the uF range, so this is not familiar.

Also, I think I got the resistance wrong on R8; I got a 330 Ohm resistor instead of a 330K resistor. Am I correct in assuming the 120R resistor is just 120 Ohm? I've also never heard of an R after the value, so I assumed he meant a 120 Ohm rating.

USS Atlantis · Post by **USS Atlantis** » Sat Feb 18, 2012 10:15 am

MillenniumFalsehood wrote:About the switching diodes: what are those exactly? Would they prevent the circuit from working properly?

Signal diodes are used to block current flow in one direction, in timing circuits they can be used to invert the timing sequence - using a different type of diode can cause the circuit to malfunction.

MillenniumFalsehood wrote:So they're not 10uF; I misread them. What is 10nF? I've only seen ratings in the uF range, so this is not familiar.

nf is nano-farads which is 1/1000 of micro-farad (mf)- using an mf rated cap instead of an nf rated cap can affect the timing as well - also there's pf - Pico-farad - which is 1/1000 of nf - so if you find 10,000 pf caps, those are equivalent to 10nf

MillenniumFalsehood wrote:Also, I think I got the resistance wrong on R8; I got a 330 Ohm resistor instead of a 330K resistor. Am I correct in assuming the 120R resistor is just 120 Ohm? I've also never heard of an R after the value, so I assumed he meant a 120 Ohm rating.

The 'R' after a resistance value is also how the Brits indicate an Ohms rating

So a 120R resistor is indeed a 120 Ohm - and using a 330 Ohm instead of a 330k will indeed affect the timing as well

MillenniumFalsehood · Post by **MillenniumFalsehood** » Sun Feb 19, 2012 2:58 pm

This is a big help. Like I said in the other thread, I'm a novice in electronics, so any help is appreciated.

In that video, it looks like he's using glass diodes. I'll try a couple I have in my parts bin (I know they're not Zener diodes).

Sloucher · Post by **Sloucher** » Mon Feb 20, 2012 8:16 am

Hi MF

Sorry I didn't see your posting earlier! Thats my circuit you've used there. I actually revamped this circuit just after the one you saw (see here for the newer one: http://modelslouch.wordpress.com/2010/1 ... o-circuit/. R3 and R4 are misplaced on the circuit you've been using and I tweaked a couple of values (sorry

)

Just to confirm what USS Atlantis was saying, in Brit-speak, R means ohms, K means kilohms and 40K2 would mean 40200 kilohms for example. Mainland Europe forced these things on us - honest!!

He's perfectly correct about the cap ratings as well. The diodes ARE 1N4148s. The diode D2 was to cut down on the red flash fade down time by the way.

Funnily enough, I've revisited this circuit myself just recently as someone wanted a single torpedo version for a BOP, so I breadboarded it again just to remind myself of its structure and it worked just fine. I then etched a pcb to hang it all on and soldered it up. Guess what? It didn't flash!! Give me a day or two and I'll get it all sorted and report back.

Bernie

Sloucher · Post by **Sloucher** » Tue Feb 21, 2012 6:18 am

@ Millennium Falsehood

I've just breadboarded the circuit again and I can confirm that this version:

http://modelslouch.wordpress.com/2012/0 ... o-circuit/

will work just fine

. There are a couple of values that are different from that original circuit, but its mainly the same. Most of the resistor values can be varied to achieve different effects (speed of fade-up/down etc). The main difference is the position of the resistor across pins 1 and 2, that was definitely wrong on that original circuit - sorry for that

.

This later design also has an extra switch and two sets of leds added so as to simulate two torpedo launchers

.

HTH

Bernie

MillenniumFalsehood · Post by **MillenniumFalsehood** » Wed Feb 22, 2012 8:54 pm

Thanks for replying! I didn't know you were an SSM'er, though I should have guessed.

Anyway, I think I'll rebuild the circuit using the new diagram (and reorder the *correct* capacitors, and other components

).

Sloucher · Post by **Sloucher** » Thu Feb 23, 2012 3:49 am

Glad to help!

BTW, I see you are using a 6v supply, so you might want to change the value of R11 from 560 to 220 ohms and change R12 from 470 to 120 ohms as the original values were for a 12v supply.

This is what the circuit looks like transposed onto an etched pcb (and filmed in the dark!!):

http://youtu.be/esdrOOwXV-c

Bernie

MillenniumFalsehood · Post by **MillenniumFalsehood** » Wed Feb 29, 2012 4:05 pm

I'm still designing the lighting circuit for my model; the 6V input was just what it called for in the drawing.

I'm ordering the new components; I'll let you know how this one works.