No, it's perfectly normal - pulsing 10 displays at 200mA gives an average of 20mA, which is pretty well spot on for the displays.Originally Posted by Sceadwian
IR LED's in remote controls are pulses at 1 amp upwards with no ill effects - it's all down to 'average' current.
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk
Sir you add 7 NPN transistors to the output of the 4511 (via Base resisters) & give Emitters as outputs to the SSDs & Collectors will goto VDD via separate current limiters.
Ah, okay, thanks.
If anyone else has some input please share itAs I mentioned earlier I will get to try these ideas out tomorrow at class.
It's not JUST average current Nigel, you pulse too much current through a P/N junction the junction will vaporize outright, the heat can't dissipate fast enough, even if the average is within it's tolerances. But I didn't know remotes used 1 amp pulses. I've always been afraid to do anything over 200ma's for any LED, but I believe ya =) If the transistors can handle it it's the easiest sollution.
Latching shift registers is the other, but that requires more IC's. They're pretty simple Dan, you shift bits into the registers one at a time via a clock line, and then when you trigger a certain I/O line those bits are all pushed out onto the IC So you can update a theoretically infinite number of I/O lines by chaining them together, it's limited only by the speed you can clock the serial data in. I dug around on Digikey and found this one.
http://www.toshiba.com/taec/componen...c//151/397.pdf
But that's just the first one I found.
For 70 elements (You're doing 10 7 segments right?) you'd need 9 of them.
Which would put you out all of 5 bucks total.
"Because I be what I be. I would tell you what you want to know if I
could, mum, but I be a cat, and no cat anywhere ever gave anyone a
straight answer, har har."
Yes, I'm aware of how LED's die
Perhaps I'd better explain further - you must use SHORT pulses - 10 seconds ON and 90 seconds OFF wouldn't do it much good
But for a remote control you're sending short bursts of 38KHz - so ON for 26uS, then OFF for 26uS - repeat this five times or so, then have a longer 'rest' with it OFF for 100uS-200uS.
It's all about heat - letting it cool down between pulses stops it getting hot and dying - which is why you can't use long pulse times.
For multiplexing displays it has to be done fast enough for it to look continuous, so increasing the current by the number of displays isn't a problem, as the pulse time is short, and the rest time long. Automatically as the pulse current goes up (becasue you're adding more displays), the pulse time goes down, and the rest time increases - keeping the heating at the same level.
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk
I've always been curious how to calculate the maximum pulse for an LED though Nigel. I mean how much peak current can you really toss through a common white LED if you can pulse it fast enough? I mean if you can calculate the maximum energy the junction can withstand you could charge a small capacitor up to a very high voltage for some insane pulses. Something I've always been curious about, I just don't know what the real limits are. I got a bag full of LED's would be fun to see what the highest power pulse I could get out of one is for strobe photography.
"Because I be what I be. I would tell you what you want to know if I
could, mum, but I be a cat, and no cat anywhere ever gave anyone a
straight answer, har har."
Elektor did a project along these lines Clicky. I can't remember the details but I seem to remember it discharged a capacitor through the LEDs to get a large current for a very short period.
Mike.
I got nothing to do today, a bag full of LED's to burn and a flash charger that will go up to 300 volts. Maybe I'll play around some =) That ring flash looks very nice, I'll book mark it. It's happening again though =O I get so any bookmarks from this website you should see what I have...
Last edited by Sceadwian; 26th March 2009 at 12:28 PM.
"Because I be what I be. I would tell you what you want to know if I
could, mum, but I be a cat, and no cat anywhere ever gave anyone a
straight answer, har har."
I was about to look at the article but it requires 10 Elektor Credits.
Do you get credits when you register with their site or do you have to purchase them? Sounds silly because I could register and find out, but I would rather not.
Silly me
Register now for ELEKTOR.com – the world-leading network for electronics and receive 10 free Elektor Credits. Subscribers to the magazine get 30 Credits! Elektor Credits allow you to download a pdf version of any magazine article. After successful registration, you also have write/reply/create topics rights on our forum as well as access to the news archive.
Please post questions to the forums. PM's are for personal communication.
BCHS/3v0's Tutorials
Junebug USB PIC programmer kit., USB Bit Whacker,
The 15 Minute Printed Circuit Board! (+drill time)
Just found the magazine and the unit uses a HV unit from a disposable camera. The unit contains a 160uF capacitor that's charged to 300V. The cap is discharge into 32 white LEDs with a 470Ω 5W series resistor. From the text it states that 10 1/100th of a second flashes can be fired before you have to worry about recharging the capacitor.
Mike.
I was thinking more along the lines of a couple tens of micro seconds for a strobo scope like app.
"Because I be what I be. I would tell you what you want to know if I
could, mum, but I be a cat, and no cat anywhere ever gave anyone a
straight answer, har har."
Re-reading some of the posts I got back to this one. This idea sounds more or less like placing a seperate 4511 for each 7-segment display and removing the resistors. We could then use the latch in the 4511 to make sure they're turned on all the time, thus elminating the dim LED's.
If none of the other methods work we'll probably end up doing that.
No base resistors required here.
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