LED prop project for a Dr Who double

Wendy

Joined Mar 24, 2008
21,848
Think about dropping the LED currents for the 4/20 circuit. High efficiency LEDs are very bright, it might not be that noticable.

Wookie, can we use a standard CMOS invertor for a driver on the MOSFETs, or is shoot through going to be a problem? I know Fenris doesn't have time at the moment, but it's a thought.
 

SgtWookie

Joined Jul 17, 2007
22,201
Think about dropping the LED currents for the 4/20 circuit. High efficiency LEDs are very bright, it might not be that noticable.
The blue LEDs he's considering are standard LEDs, in the 45-65 mcd range with 20mA current. They won't be very bright even at full current.

Wookie, can we use a standard CMOS inverter for a driver on the MOSFETs, or is shoot through going to be a problem? I know Fenris doesn't have time at the moment, but it's a thought.
Well, I suppose a 40106 or 74HC14 hex Schmitt-trigger inverter could be used (with suitable resistor on the gate) to drive a 2N7000, or something similar - even a fairly high-gain BJT. Not quite sure what you have in mind.
 

Wendy

Joined Mar 24, 2008
21,848
A CMOS 555 should be able to drive two complementary MOSFETs, similar to what is in a CMOS invertor. I was thinking in terms of a driver similar to my other BJT approach, but without the zeners.
 

SgtWookie

Joined Jul 17, 2007
22,201
A CMOS 555 should be able to drive two complementary MOSFETs, similar to what is in a CMOS invertor. I was thinking in terms of a driver similar to my other BJT approach, but without the zeners.
OK, I see where you're going.

Seems that the CMOS 555 versions have asymmetrical current source/sink capabilities, and one of them is considerably less than the other.

The big problem Fenris is facing with the 4-timer 20-led circuit is the current draw. Even if it were reduced 50%, you'd still have 100mA current just in the LEDs alone - and they'd be mighty dim. The 555 timers would add some overhead, but that basic 200mA draw for full intensity on the LEDs would pull a 9v transistor battery flat in very short order. Decreasing it to 110mA or so would certainly help a great deal.

He'd be much better off if he could use a few AA batteries with the inductive boost to drive LEDs in series; current utilization would be considerably less, with greatly extended battery life. Unfortunately, that would likely make your 4-20 circuit impractical.
 

Wendy

Joined Mar 24, 2008
21,848
I was playing with the LEDs (and this tester), they are plenty bright even at 2ma. As I understand it, the OP time line is too tight to work with, but I might be able to help him getting some.
 

Thread Starter

Fenris

Joined Oct 21, 2007
288
Hi Guys

I have the components to make the 2 4017 chaser circuits. I had a near miss today when my laminator decided to jam up. I managed to pull the board out and luckily everything was stuck down.

I am using semi-gloss photo paper now which comes off very nicely indeed.

So I have 2 PCB's and I just need to whip them through a bandsaw to cut them to shape. I shall continue with this tomorrow :D

regards

Fenris
 

Attachments

Wendy

Joined Mar 24, 2008
21,848
For what it's worth I mailed 44 of the suckers to ya about 2 hours ago. The mailing costs were a lot less then I thought.

I mentioned what I was doing to the lady what I was doing. Since for her mailing was routine she did it while I waited. I threw one of my introduction cards (like business cards, but I have nothing to sell) in the static bag. PM me your email address please.
 

Thread Starter

Fenris

Joined Oct 21, 2007
288
Hi all

the circuit boards got bandsawn today and drilled. At this point I have the resistors, 2N7000 mosfets and the Blue LED's fitted to both boards. I have to get the IC sockets, which I forgot, so I can fit the 555's and 4017's. Fingers crossed sometime tomorrow I will have a pair of LED chasers spinning in anti-phase and a small sub-circuit beeping. 2 switches and pots will be used to control/interact with the prop.

I have test fitted the 2 PCB's in their future home and everything fits! The battery holder is bolted to the inside of one of the caps and passes easily between the 2 boards. They are held apart/together by 4 pillars of single core mains wire. The sheathing of which is used as the spacer.

I hope it works :D

regards

Fenris
 

Attachments

Thread Starter

Fenris

Joined Oct 21, 2007
288
Hi Guys

I have just completed the primary PCB. Thats the one that has all the chips on it as well as it's own mosfet/LED's. I am pleased, nay re-leaved, to say that it is working no problem.

Thanks for all the help and suggestions thus far chaps. Now I must nip off and get the second PCB wired up. Photos later!

Regards

Fenris
 

Thread Starter

Fenris

Joined Oct 21, 2007
288
Hi all

Well the circuit was built and finished in fairly short order. Fitting it in it's permanent home proved to be the most utterly, utterly, utterly frustrating bugger of a job!!!!

But it is now all finished and, I am glad to say, working perfectly. The Blue LED's are stunning IMHO. I have more on the way from Bill for another project and if that goes as well as this one it'll be great!

Here is a link to a poor quality video of it doing it's thing. Tomorrow I only have 2 of my Voice mods to build and get out to the guys before friday :D Busy, busy, busy!

A big thanks to all of you who advised encouraged and put up with my dumb questions.

http://s200.photobucket.com/albums/aa97/Fenris_2007/?action=view&current=SV600194.flv

regards

Fenris
 

bertus

Joined Apr 5, 2008
20,049
Hello Fenris,

The prop looks nice.
Great job together with the guys (Bill and Wookie) from the AAC.

Greetings,
Bertus
 

Thread Starter

Fenris

Joined Oct 21, 2007
288
Hi Bertus

Thank you :) I owe a lot to the guys for sure. With out their help I'd have got no where!

The prop is currently sat next to me 'doing it's thing' :D

BTW Bill I have a pair of 556's to start trying out the 4/20. I wanted 4 555 of course but apparently Maplins policy is to stock only 2 of anything so I got the dual package which will be fine to get going with................ They are becoming a bit pointless in this department IMHO.

In light of that as I will likely do a new PCB pattern to suit have you a preference? The 555 x 4 layout or a 556 x 2?

regards

Fenris
 
Last edited:

Wendy

Joined Mar 24, 2008
21,848
I'm not picky, I'll go with whatever.

Nice job, BTW. I'm looking for what else you come up with.
 

Thread Starter

Fenris

Joined Oct 21, 2007
288
OK Bill ;)

Just a quick question as regards this alternative chip form. You advised me to fit .1uF ceramics across the supply of each of the 555's to stop the supply possibly syncing the chips. Obviously this is good practice anyway so I will fit a cap across the supply of each of the 556's.

I take it that each half of the 556 will maintain it's independence as regards the sharing of the supply. I am probably over thinking this :D I hope I explained myself well enough there.

I sat down last night and, hopefully, drew up the circuit of the timing components around a 556. I had the pin outs for a 555 and the 556 in front of me so I could identify the corresponding pins between the two and hopefully I have drawn it up OK thus far:D . I am going to bread board it first and try it out with the red LED's I have to get an Idea of the visual effect. Then I will draw up the circuit proper.

regards

Fenris
 
Last edited:

Wendy

Joined Mar 24, 2008
21,848
Check out this data sheet I made, it's handy for those kind of jobs. My PaintCAD is also meant to be a general reference.
 

Attachments

Thread Starter

Fenris

Joined Oct 21, 2007
288
Hi Bill


Thanks for that. Duly saved to my electronics folder. Pleased to say I had it right having used your reference to check it ;) . I know it's easy stuff but I worry constantly!

BTW Big Blue (The Prop) still going great! I presume from the gate resistor to the Blue LED I could transfer that part of the circuit to other IC's. Like a 7 Segment Display driver chip to use in a similar fashion.

I am starting to bread board the circuits :D

regards

Fenris
 

Wendy

Joined Mar 24, 2008
21,848
Just curious, what do you use these props for? Parties? Or are you providing stuff for the show on the side? :p
 

Thread Starter

Fenris

Joined Oct 21, 2007
288
Hi Bill

For the show! If only, IF ONLY! The chap it's for acts as the current incarnation of the Dr (David Tennant) and he performs where ever he is requested. This is mostly all for charity. Usually surrounded by Daleks as well :D . He originally wanted 2 of the gadgets from the series but was let down. They are just to add to the overall 'show' and it helps engage the kids and punters of course.

A group of Daleks at a show are known collectively as a 'trundle' :D

Any way I have newsssssssss!

I have built the 4/20 or at least considering the chips I'm using 2/20. Once I corrected 3 wires from the LED's and added 4 wires to the chips it all started working properly :D . 10 Red LED's and 5 Blue are used. I have them set out like a Christmas tree, the same as your schematic.

It looks brilliant! I really like the effect. Resistor wise I only had one value the same as the timer resistors. So I am using 47K, 56K, 68K and 82K. All the LED's are nice and bright on/off. There is also the odd few that go half bright which I guess is where the electrical path passes through a few of the resistors on the way. I love it :D

I guess the other thing to have a go at is variable resistor to play with the timings. Great circuit Bill! :D

http://s200.photobucket.com/albums/aa97/Fenris_2007/?action=view&current=SV600195.flv

The video doesn't do it justice due to the slow CCD of my camera but you get the idea.

regards

Fenris
 

Attachments

Wendy

Joined Mar 24, 2008
21,848
Coolness. I think some of the LEDs need separated, it would increase the randomness (which is illustionary).

I've been thinking of making one that is on a grid, maybe going for a From 6, 42. My thought is if you giver the timer a knob to adjust the rate (6 total), it would make a decent busy box. I have heard autistic kids love flashing lights, especially if they have hidden patterns (and they can adjust them too).

Just a thought.

Thanks for showing your project. Do I notice a certain Christmas Tree shape? :) That is one of my other thoughts for this concept.

BTW, just finished my Long Duration Blue LED Flasher article. Now to see how long it lasts. My simpliest red LED version is still going, though dim, since Feb. 22 from a pair of "AAA" batteries.

We can hear the missus in the background. What does she think about your hobby?
 
Last edited:
Top