picbits

If $$$ are an issue then go with the Microchip PIC. You can get free samples from Microchip (please please please don't abuse this service though as it ruins it for the genuine samplers). Programmers can be knocked up for a couple of $$ from the millions of available "free" programmers.

I'd suggest using something like an 18F1320 to start off with - reasonable amount of pins, easier to program than the 16F series, internal oscillator, less gotchas. If you're sampling then also go for the 18F452 (40 Pin). If you're feeling very adventurous, get hold of a MAX232 and you can make your own bootloader with the 1320 and serial program it in circuit but thats a bit more advanced.

My favourite processor is the 18F1220/1320 for prototyping (and many finished products) - they are just so easy to use and fairly cheap.

seveprim

First I am not a fan off the single pin per led ... just stated for the noob ... second LEDs can happily be pulsed at higher currents as I have indicators running 24 hr 365 days for over 6 yrs and never suffered any led failure(80 milliamp pulses that is 4 times the maximun DC rating but the average is far less then 20 ma )

if in doubt look how they drive IR leds on your TV remote(2 amp pulses) thirdly you dont need 50 times the current forth you can always run high brightness leds requires less current for a given brightness ...

and what the hell is charlie plexing .. lol

If you read back you noticed I stated mulitplex is the way to go if you know how ...

Nigel Goodwin

But that's only FOUR times, you were suggesting pulsing the LED's (and the drivers) at fifty times the current.

I'm fully aware of pulsing LED's, and my tutorials even explain it - but you still need 50 times the current for the same brightness if pulsing them at 1/50th duty cycle. If you're comparing high brightness LED's with normal ones, then it would be somewhat less - but if you were using high brighness ones to start with, it's still 50 times the current for the same brightness!.

Perhaps you should google it?, or even search here for the many examples of it - I'll give you a clue, a guy called Charlie invented it (or at least is credited for it), I believe he worked for Maxim?.

Yes, as did I, but then you suggested multiplexing 1x50 to save 49 resistors - which was really getting rather silly?.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

charlie_r

@picbits- i will probably do the microchip routine, and will build the inchworm+.

Further down the road, I'll also try out the AVR system as well, as I may find apps I want where that would be more suitable. I don't want to be locked into one system.

On further reading about the picaxe, I finally saw that it is the microchip with bootloader already installed, so I assume fuses would be already set, unless I'm still confused. Or is the fuse thing AVR? Must do more reading!!

Next question- For keeping current down, can I connect the output pins to a pair of switching transistors npn (source) & pnp (sink) to handle the higher currents to drive the LEDs?

eblc1388

Warnings: Moving to AVR is a one way street. Very few would turn back to PICs again after the experience.

__________________
L.Chung

seveprim

But the AVR streets are paved with gold why would one turn to the cobble stones of a PIC!!!

charlie_r

from what i've seen so far, each has it's place.

seveprim

Never did I state 50 times the current you assumed that. You can quiet happily pulse them at high rates of current (I have found about 4 times the rated current) at high speed and not notice any real difference in brightness (dont forgret the human eye will think it is still on and if its bright enough over stimulate it (look at bright light the light it stays on well after you look away well your eyes tells your brain there is still light there) so it is all about what the human eye can detect. Dont beleive me try it for yourself

50 leds and resistor and a MCU of your choice go kill a few hours.

So in breif any led pulsed at resonable speed and 4 times it DC max current will look very bright(close to full brightness) and you would never be able to tell so you only need 4 times the current which is then averaged over x leds per second !!!

My Indcators run at 12-30volts 60milliamps (DC average)taken directly from power source they can be seen over 20 ft away (daylight) and drive total of 70 leds ) Note 20 milliamps is consumed by the micro so the leds average is about 40milliamp.

Nigel Goodwin

While they may be of acceptable brightness they are NOT the same brightness, and you could run individual LED's at lower power to give the same brightness level.

And from what I recall about multiplexing studies in the past, once you get to very low duty cycles you have to INCREASE the current pulses substantially to maintain a similar brightness level.

My 64 LED array is clearly visible in a bright indoors over 10m, but I've never tried it outside, nor have I bothered measuring the current taken - but they are driven solely from a PIC, no drivers.

Presumably your 70 LED's are multiplexed?, and not 1x70, so it doesn't really prove anything about your silly 1x50 suggestion?.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

seveprim

Yes I do multiplex them .. this is getting a little rediculus the tic for tac... I am not trying to defend single pin per led nor 1 resistor for 50 leds just informing ppl you can get away with it however it is not the ideal solution nor is there any set rule to say this is how it must be done... at the end of the day if ya see the LED light up and ya happy and it dont blow up then it is correct !!!

Nigel Goodwin

My point through out has been that it was a completely silly suggestion, it's not practical, and only a complete idiot would 'use' such a scheme.

Bear in mind these threads and posts are permanent, posting such a useless idea could well make some beginner think it's a practical suggestion! - when (as you appear to agree?) it's completely non-practical.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

charlie_r

Guys-

I didn't mean to open a can of worms here!

I would be perfectly satisfied with 1 LED driver per output, or mutiplexed.

attached is what I think will work for me.

I haven't looked at the datasheet for this particular pic, I just grabbed an 8 pin at random. I could just as easily grabbed an ATtiny for this example. I purposely didn't complete the diagram, and won't until I check the datasheets on a few.

What I need to know is if I'm on the right track or not.

Attached Images

pic1.jpg (34.2 KB, 15 views)

Nigel Goodwin

That's fine, depending what you want to do - however, it's usually far better to have the LED's fed from the collector of the transistor (much less loss), with resistors feeding the bases.

But is five outputs all you're wanting?.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

charlie_r

That was just an example of what I want. I will probably do more. I am thinking of a relatively long light bar with 15 of those 4 LED sections, and program the pic with two inputs, one for left turn and one for right, controlled by an SPDT switch. Will have to put a "debounce" circuit on each input, might use 555 monostable for that. Unless I can figure out how to use a logic gate for that.

Nigel Goodwin

The whole point of micro-controllers is to make your design simple, cheap, and far more effective. You don't need to add extra devices to de-bounce switches, you do it in the software. To reduce I/O requirements, for 15 LED's multiplexing would probably be a good idea - details for 64 LED's are in my PIC tutorials.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk