I think this project would suit a micro-controller, but I just wondered if there was a simpler way to add flashing all ON/OFF function to a 20 LED chaser/scanner circuit (2 decade counters).. by just connecting say two sets of 10 outputs in parallel (from WHAT?). It all has to fit in hat.. thanks.

 

I suppose the simplest is just clock the frequency up so they all look like they are on at the same time.. I think that is my plan B. But I would be interested in any ideas.

 

I suppose the simplest is just clock the frequency up so they all look like they are on at the same time.. I think that is my plan B. But I would be interested in any ideas.

Actually all that is needed is a separate transistor connected in parallel to the tail of each LED and driven by another logic chip or perhaps a JK Flip Flop one output for each set of 10..

 

Brilliant.. I think I have it.. Not sure if a JK Flip Flop output pin can handle 10 transistors BUT all I need is a couple of discrete component Astable or is it Unstable multivibrator flip flops.! And I have the perfect starter kit. In 1965 I was in year 8 at high school and we were given an electronic transistor project.. A competition put on by the Amalgamated Wireless Valve Company (AWV) called Operation Multiflash.. the prize was "An AWA transistor portable radio and a visit to the transistor and valve works of the Amalgamated Wireless Valve Co. Pty. Ltd." The demise of the valve initiated the name/logo change from AWV to AWA around that time.

I did not enter the project or build the kit so I still have the original supplied kit. It comprised the instructions, conditions of entry and the all important three (AWV) AS28 metal can transistors in a plastic bag stapled to the back. The closing date for entry was the 8th September 1965. I don't think printed circuit boards were invented then.

It was presented by the 'Science Teachers Association of NSW' at the "SCIENCE IN THE DEVELOPMENT OF AUSTRALIA EXHIBITION" held at the Sydney Showgrounds from the 11th-19th August 1965. Either way I think it fitting that I now want to use it to jazz up an accedemic 'mortar board' hat. Ha Ha..

 

A J-K FF might drive one LED or one string of LEDs at low current.
In present chaser setup is more than one LED on at a time? Do you have a schematic ? If running chaser at high speed, will LEDs be bright enough?
If present system uses a 4017 or something sim. pulsing the reset with a 555 might give desired effect- one LED might remain on.
Just guesswork with out more inf.
Believe PCBs were around in 1950s, Si transistors 1960s, ICs mid 1960s- from slipping memory.

 

A J-K FF might drive one LED or one string of LEDs at low current.
In present chaser setup is more than one LED on at a time? Do you have a schematic ? If running chaser at high speed, will LEDs be bright enough?
If present system uses a 4017 or something sim. pulsing the reset with a 555 might give desired effect- one LED might remain on.
Just guesswork with out more inf.

Hey thanks.. The circuit actually uses just one 4017 with each output driving a BC548 via a 10K-R which then switches 2 LED's at once. They stagger the wiring so 0 - 5 runs one way and 6 - 9 runs back. Each pair of LEDs interleaves the other return pair. Another problem is isolating the LED's on a light strip. I want to leave the 12 volt bus and just break the earth links but after cutting one it didn't isolate it it just stopped working from one end.?

 

The GND(earth link) is the common pin, so you can cut if off, the only thing you can do is cut the 12V pin.

Unless you separate them to 10 different pieces.

 

Two LEDs on at a time out of 20 might not be verry bright but if you can change clock could be worth a try.

 

I recently made a 18 LED flashing ckt. for a costume hat. Surface mt LEDs with 100 ohm 1/8 W / LED all in 4 position AA battery box with switch. One position shorted & used for ckt.; could have been AAA box. Can draw it up if interested.

 

The GND(earth link) is the common pin, so you can cut if off, the only thing you can do is cut the 12V pin.

Unless you separate them to 10 different pieces.

Thanks.. I have decided to go with groups of 3 instead of single LEDs.. the strip is designed to be cut that way..

 

I recently made a 18 LED flashing ckt. for a costume hat. Surface mt LEDs with 100 ohm 1/8 W / LED all in 4 position AA battery box with switch. One position shorted & used for ckt.; could have been AAA box. Can draw it up if interested.

Thanks so much.. my LED strip is designed to be cut in groups of 3... I don't really have the time to do anything too fancy.. so I'll go with that. By alternating groups of 3 LEDs and driving 2 off each transistor I can sequence flash all 60 LEDs in two groups of 30 from a single decade counter. I also discovered that turning on all 60 LEDs will draw about an amp which is way too much for my battery capacity visa-vi required service time.

 

One question I still have which bothers me.. LEDs are used for their compactness, brightness and efficiency.. ok. But to drop 12V down to 2V with a series resistor surely defeats the purpose. Last time i checked I think power was (P = I^2 x R) so in any such circuit the power drain to the series resistors is 10/12 of P while that delivered to the LED is only 2/12 of P. So why don't the resistors get hot and how does that effect the idea that these things are efficient. Surely wasting 10/12 of your power should demand a better circuit or something??

 

Attach a schematic is more easy to discussing.

 

We started with 20 LEDs now we are up to 60? Where was it suggested to run a single LED from 12 V? From post 11 average current should be about 40 mA .

 

Attach a schematic is more easy to discussing.

Sorry the schematic I have is for a 20 LED Light Scanner Chaser kit using a 555 timer clocking a 4017 the outputs driving two LEDs each through a BC548. They get the chaser effect by simply arranging the physical order of the LEDs 0 - 5 up and 6 - 9 back the pairs of LEDs overlap each other.. Unable to connect scanner since upgrading printer!!

 

We started with 20 LEDs now we are up to 60? Where was it suggested to run a single LED from 12 V? From post 11 average current should be about 40 mA .

Thanks so much for your help. The project is to put a line of LEDs around the edges of a graduation mortar board hat. The original idea being to be able to switch a number of different pattern effects from chasing change direction and flashing etc. I purchased a led light chaser kit as the basis. It soon became apparent that flashing all was incompatible with sequential chasing and may draw too much power from my battery supply. So I have ditched the idea of flashing and just want to go with chasing back and forth etc.

The kit started with 20 red LED's, not bright enough for the application. So I purchased a 60 LED 12V light strip and hoped to separate out the required LEDs and address them as per the kit. But then found I could not easily separate individual LEDs. But I can get separate groups of 3. Next came the question how many can I drive.. of course I wanted to use as many as possible. Since the original kit drives pairs of LEDs through BC548 transistors I was told this trany could sink nearly an amp and the kit notes said brighter LEDs could be used. So enlightened with that knowledge I thought I could probably drive 6 LEDs from each BC548. So by arranging all 60 LED's in a chaser fashion arranged as two sets of 10 x (group of 3) set out alternating in opposite order of switching that would be ok.

So if the BC548 can drive/switch 6 white LEDs at a time it should work.. shouldn't it?

 

Really, a schematic will help. Necessary to discuss your questions. Sketch it and take a pic with your phone. Or use a program like MS Paint and draw it out.

Driving six LEDs depends on how they're wired to the transistor.

Also, how do you make the leap of faith from two LEDs in a pair to six? I for one am confused.

 

cmon, just use 4017 decade counter /decoder, clock it whatever you want (555), for each output connect two LEDs. in fact you can connect more than 2 LEDs if supply voltage is high enough...
http://www.allaboutcircuits.com/vol_6/chpt_7/6.html

 

Attach a schematic is more easy to discussing.

Thanks.. but my reply to you about 14 hours ago seems to have disappeared. In that reply I said I had upgraded my printer but I cannot get the scanner working on this computer.. Best not to go there.. have a nice day.

 

Thanks.. but my reply to you about 14 hours ago seems to have disappeared. In that reply I said I had upgraded my printer but I cannot get the scanner working on this computer.. Best not to go there.. have a nice day.

Really, a schematic will help. Necessary to discuss your questions. Sketch it and take a pic with your phone. Or use a program like MS Paint and draw it out.

But you don't need a scanner for a schematic of the circuitry being used to drive the LEDs. Or take a picture with a smart phone and attach it. Multiple pictures if necessary.