max power limit propeller chip

zapmaster

In the specifications of the propeller chip.
max current is 300ma.
pins can source/sink 40ma.

i want to light 18 indepent led's with pwm up to 35 ma each 630ma total.

can i sink them with the pins.

with a seprate 5v power supply.

will this be ok for the· propeller chip?

·

jknightandkarr

Just to be safe I'd use transistors to power them & use the Propeller to activate the leds.

Joe

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
I'm going insaine. It's SOOOOOO much fun. lol

zapmaster

That does not help. (but thanks it would be the safe way)

I want to know if it·will burn up the chip?

the chip will still be drawing 35ma. well under 300ma

but the ground bus will have the 665ma.·(can it take it)?

I want to make this with as few componets.

Tapperman

zapmaster said...
In the specifications of the propeller chip.
max current is 300ma.
pins can source/sink 40ma.

i want to light 18 indepent led's with pwm up to 35 ma each 630ma total.

can i sink them with the pins.

with a seprate 5v power supply.

will this be ok for the· propeller chip?

If you don't mind adding·three chips, use 4049's (Hex Inverting buffers) ... this will handle the voltage stepup from 3.3 to 5v, and also remove the current from the propeller.·

zapmaster

Thank you but i just read the data sheet that device(that i found) only handles 5 ma output at 5 v.

http://www.jaycar.com.au/images_uploaded/CD4050BC.PDF

I have a workaround i just want to know if i can do this.

when i'm done i'm going to have 156 led in this system. dmx controled

i set this up once with a bs2e talking to max6956 talking ic2 but the distances 1000' was to long.

Miner_with_a_PIC

Zapmaster, if the propeller specification says 300 mA then 300 mA it is...going outside this range and damage may occur. The concern goes beyond power handling capacity and falls under the umbrella of IR drop from pin to die (little metal wires connect these) and the IR drops related to the metalization on the die. These IR drops could lead to chip lock-up or frying of the logic downstream from the PLL (I believe this is a prop1 vulnerability caused by VSS to VSS or VDD to VDD voltage deltas). If you can craft your project so that not all 18 LEDs are energized/pulsed simultaneously you might be okay.

One follow-on thought...you may buy yourself extra breathing room if you source 9 LEDs (common ground) and sink the other 9 LEDs (common Vcc). In this way the IR drops would be distributed between the VSS and VDD.

Post Edited (Miner_with_a_PIC) : 2/20/2010 9:46:43 PM GMT

Mike Green

@zapmaster - The specs you're quoting are absolute maximums. As far as Parallax is concerned, there's no wiggle room. You may get away with exceeding them. You may get away sometimes. There's always chip to chip variability. The room temperature can vary and that can affect things. Too much current and too much heat can shorten a chip's lifetime. Maybe it'll work for 6 months, then fail. Maybe it'll work for a couple of hours or days. Generally it's a bad idea to push the limits of a device.

zapmaster

Thanks for the support. Confermed my fear. Darnit.

Tapperman

zapmaster said...

Thank you but i just read the data sheet that device(that i found) only handles 5 ma output at 5 v.

http://www.jaycar.com.au/images_uploaded/CD4050BC.PDF

I have a workaround i just want to know if i can do this.

when i'm done i'm going to have 156 led in this system. dmx controled

i set this up once with a bs2e talking to max6956 talking ic2 but the distances 1000' was to long.

I'm currious, is it possible to use leds which use less current?· I mean, if you can't raise the bridge, lower the river.· BTW, what sort of project is it?· I'm currious about the 156 LED's.· Are they arranged in an array?

10gigbill

I'm driving 30 Led's from the prop and using 4 ULN2803 chips... no worries. You can drive several hundred ma per pin.





Bill

zapmaster

Tapperman said...

zapmaster said...

Thank you but i just read the data sheet that device(that i found) only handles 5 ma output at 5 v.

http://www.jaycar.com.au/images_uploaded/CD4050BC.PDF

I have a workaround i just want to know if i can do this.

when i'm done i'm going to have 156 led in this system. dmx controled

i set this up once with a bs2e talking to max6956 talking ic2 but the distances 1000' was to long.

I'm currious, is it possible to use leds which use less current?· I mean, if you can't raise the bridge, lower the river.· BTW, what sort of project is it?· I'm currious about the 156 LED's.· Are they arranged in an array?

I have a very long driveway 630' with horse fence 6000v(had to add zeaner diodes). I'm going to have a ping pong ball on each post with a tricolor led the post are 12' apart. Doing a light show to advertize my farm. Also this will be connected to my sign. I have had it working with a bs2e but it is a little slow and now that I’m learning the prop I’m giving that a go.
I’m also in the flight path so I hope not to have accidental landings.
the master prop will be sending signals using dmx for the long run.

Tired2

Excellent project idea, you should post some pics/video when you get it working.

I have used the td62783a 8CH non-inverting Octal buffer for a while now, with great results. It is similar to the ULN2803's mentioned previously, but it is a high side driver, so it sources instead of sinks (I think I said that right)... The current is 500mA per channel, and is happy with a 3.3v input, and up to about 35v at vcc.

I might suggest wiring the chip with 12v or more, and use an appropriate current limiting resistor. DC does not travel as well as AC over long distances, so to compensate for that, a higher voltage at the input should result in a higher voltage at the output... You should be able to calculate the resistance of the wire at each pole based on the length of wire leading up to it to find the voltage drop across the line.

Another option that you should consider if you are already adding extra chips, is a shift register.

Check out this object in the obex:

http://obex.parallax.com/objects/437/

74HC595 Regular and MultiPWM Shift Register Driver

It will give you 8 outputs at 20mA per chip output, which may not be enough... maybe you should go with shift registers for I/O expansion and Darlington arrays for current buffering. You should be able to get all 156 on one propeller chip I believe.

Post Edited (Tired2) : 2/23/2010 6:56:40 PM GMT

hover1

The TPIC6595 is an 8-Bit Shift Register with 250ma continuous per output. 1.5A pulsed current per output.
I have a couple on order to try out. Digi Key $3.11 each for DIP


Are you going to run dmx over RS-485 and have a prop on each end?

Jim

Post Edited (hover1) : 2/23/2010 6:10:32 PM GMT

zapmaster

Thanks for the ideas. but I wanted to produce as many colors as I could. I’m using MAX6956AAI led driver that can drive 20 led's with 16 levels of brightness. I have interfaced the max6956 with a prop yesterday and had complete success. the dmx gui I made(prop with mouse with vga) is able to adjust 4096 colors on each led. 16 red 16 blue 16 green. Thanks for the free samples max.
yes power is going to be a big issue. ·12 vdc·with a battery at the end charging during the day and at night will help power the display. each device having a 5v and 3.3v regulator.

BigFoot

If you must drive the LED's directly you should check out some of the new high efficiency LED's. Otherwise you might
want to look into water cooling the propeller chip [noparse]:)[/noparse]....

Russ

tonyp12

I'm putting together a 56LED charlieplexed display.
uses 8 pins and 8 resistors.

As only one LED is on any ant time,
when one pin is high and one pin is ground
and the other 6 pins are tristated.
It keeps the total current low,
but with as low as 2% duty they will be a little dim.

In your case I would use a 5pins for 20 LEDS
do this 6 times on the prop and it uses a total of 30 pins
Total 120 LEDS


Or you could go with 5 NPN transistors for a 20% duty
http://www.instructables.com/files/deriv/FX7/WSQ2/FHM8R2A6/FX7WSQ2FHM8R2A6.MEDIUM.jpg

P.S tricolor LED uses 3 times more pins so now you would be down to 40LEDS

Post Edited (tonyp12) : 2/25/2010 12:22:23 AM GMT