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Rayman
Registered Member

Date Joined Jul 2007
Total Posts : 2408

Posted 11/1/2009 9:57 AM (GMT -8)

Just looking at the datasheet and manual to see how many LEDs I can drive and the same time, and was a little dissappointed...

Datasheet says 300 mA total. That's not so bad, except that I want to overdrive ~8 LEDs at a time to 60 to 100 mA...

What's worse is the manual says 100 mA total per group of 8 pins. That means you can't even drive 8 LEDs at full 20 mA current, without worring about what group their in...

But, I'm pretty sure I've seen people drive 8 LEDs...

Are these limits for real?

My Prop Info&Apps: http://www.rayslogic.com/propeller/propeller.htm

doggiedoc
"I never finish anyth"

Date Joined Dec 2004
Total Posts : 176

Posted 11/1/2009 10:07 AM (GMT -8)

I bumped into this limit this past week working with some full color LEDs. I was trying to cycle 7 of them through the range of colors so that the group made a color wave. It didn't occur to me that I'd hit the current limit, but I did. 1k resistors help but at the cost of brightness.

I suppose I could drive them with a transistor but with the RGB LEDs that means 3 transistors per LED - so the component count makes it harder to breadboard.

You mentioned per group of 8 pins. I need to pull out the datasheet and rearrange the pins I'm using to see if that will help.

There are only 10 types of people in the world, those that understand binary and those that don't.

Oldbitcollector
Professional Stuntman

Date Joined Mar 2007
Total Posts : 3367

Posted 11/1/2009 10:07 AM (GMT -8)

Without knowing the rules (having missed that in the datasheet; ignorance is sometimes wonderful),
I've had no issues driving multiple LED segments along with LEDs on the Propeller Protoboard.

Haven't murdered a Propeller yet..

OBC

New to the Propeller?

Visit the: The Propeller Pages @ Warranty Void.

hover1
I have 3 Propellers

Date Joined Sep 2007
Total Posts : 371

Posted 11/1/2009 10:11 AM (GMT -8)

Maybe Charliplexing? Have not tried it yet.

http://forums.parallax.com/forums/default.aspx?f=25&m=208235&p=1&ord=a

Jim

doggiedoc
"I never finish anyth"

Date Joined Dec 2004
Total Posts : 176

Posted 11/1/2009 11:06 AM (GMT -8)

Well spreading the LEDs out over 4 groups of 8 pins didn't help. Perhaps I am mistaken.

There are only 10 types of people in the world, those that understand binary and those that don't.

PJ Allen
Counsel of Despair ???

Date Joined Sep 2005
Total Posts : 2807

Posted 11/1/2009 11:34 AM (GMT -8)

Those specs I think are for continuously on. If you're PWMing, given a reasonably quick rep_rate, then I'd figure there's some leeway.

hover1
I have 3 Propellers

Date Joined Sep 2007
Total Posts : 371

Posted 11/1/2009 12:16 PM (GMT -8)

This was the Charlieplexing post I was looking for before:

http://forums.parallax.com/forums/default.aspx?f=25&m=238027

Jim

James Michael Huselton
Registered Member

Date Joined Nov 2007
Total Posts : 613

Posted 11/1/2009 12:28 PM (GMT -8)

Hover1,

Thanks! I was just last week trying to remember where I saw the code for Charlieplexing...

JMH

Toby Seckshund
Registered Member

Date Joined Mar 2009
Total Posts : 477

Posted 11/1/2009 12:32 PM (GMT -8)

Take pity on the poor beast, and use external drivers. I have always found it so tricky to rewire the fused internals, and now the eyesights gone.

I had the same question, but the other way around, if it is ok to stress the input diodes to 0.5mA or so then is it permissable to stress them all to the limit together. But then I am somebody that run them overclocked and up at 4.2 Volts sometimes. Parallax has given us a very resilient toy.

Style and grace : Nil point

hover1
I have 3 Propellers

Date Joined Sep 2007
Total Posts : 371

Posted 11/1/2009 2:04 PM (GMT -8)

As PJ says, there is something to be said for PWM.

I did a project a few weeks ago that I had to a "wave" of 5 rows of LED's. I had 28 LED's on 5 Pins of the Prop through 220 ohm resistor packs. On two of the pins I have 9 LED's connected. I used the pwm_x8.spin object. I used these supebright LED's:

http://www.superbrightleds.com/specs/y3230_specs.htm

I had to get it ready in 1 day, so I couldn't get any external drivers for the opening night. I fully expected to have to go back and replace the Prop and circuitry, but after 6 weeks it's still running fine.

yarisboy
Registered Member

Date Joined Jul 2008
Total Posts : 52

Posted 11/1/2009 3:45 PM (GMT -8)

On the BS2 I broke my LED current budget. Instead of transistors I used quad pack op amps to drive high intensity LEDs. Be sure to bump up the trace size feeding the op amps. If you don't, you may run out of power on long branched traces. See tachometer under finished projects/industrial.

MOORE'S LAW: The capabilities of electronics shall double every 18 months.
cloyd's corollary: Hardware is easy, software is hard.

dMajo
Italy 72

Date Joined Apr 2008
Total Posts : 329

Posted 11/2/2009 12:56 AM (GMT -8)

@Rayman

the only limits I am aware of are the 300mA total (chip) max current drain on vdd/vss and the 40 mA (sink/source) per IO pin. From where the 100 mA?

Propeller Object Exchange (last Publications / Updates); Vaati's custom search

Rayman
Registered Member

Date Joined Jul 2007
Total Posts : 2408

Posted 11/2/2009 2:46 AM (GMT -8)

Manual P.15:

Pin Descriptions
Table 1-1: Pin Descriptions
Pin Name Direction Description
P0 – P31 I/O
General purpose I/O Port A. Can source/sink 30 mA each at 3.3 VDC. Do
not exceed 100 mA source/sink total across any group of I/O pins at once.
Logic threshold is ≈ ½ VDD; 1.65 VDC @ 3.3 VDC.
The pins shown below have a special purpose upon power-up/reset but are
general purpose I/O afterwards.
P28 - I2C SCL connection to optional, external EEPROM.
P29 - I2C SDA connection to optional, external EEPROM.
P30 - Serial Tx to host.
P31 - Serial Rx from host.

My Prop Info&Apps: http://www.rayslogic.com/propeller/propeller.htm

Mike Green
Registered Member

Date Joined Oct 2004
Total Posts : 13554

Posted 11/2/2009 6:05 AM (GMT -8)

The Propeller Manual was written first, then the Datasheet was written as the definitive documentation for the chip and the Datasheet only mentions the overall current limit and the per I/O limit. The statement in the Manual may be a leftover from the SX documentation, particularly since the Propeller's I/O pins are not divided up into groups the way the I/O ports on the SX (and PICs) are. Still, high output currents can cause voltage shifts across the chip due to resistance in the on-chip conductors and, the higher the current, the more careful you'd have to be with bypass capacitors and low impedance power wiring to the chip's power pins let along tighter power supply regulation.

BigFoot
Registered Member

Date Joined Jun 2009
Total Posts : 35

Posted 11/2/2009 8:59 AM (GMT -8)

Surface mount transistors are small & cheep, what are you guys waiting for ? We pay about $0.0429
for the 2N3904's from Digi-Key in 100's.

It is not a good idea to drive allot of current out of any processor. I guess it is ok for a hobby project
but if you are planning on selling thousands of propeller processor boards. forget it.

Russ

dMajo
Italy 72

Date Joined Apr 2008
Total Posts : 329

Posted 11/2/2009 12:28 PM (GMT -8)

Rayman said...
Manual P.15:

Pin Descriptions
Table 1-1: Pin Descriptions
Pin Name Direction Description
P0 – P31 I/O
General purpose I/O Port A. Can source/sink 30 mA each at 3.3 VDC. Do
not exceed 100 mA source/sink total across any group of I/O pins at once.
Logic threshold is ≈ ½ VDD; 1.65 VDC @ 3.3 VDC.
The pins shown below have a special purpose upon power-up/reset but are
general purpose I/O afterwards.
P28 - I2C SCL connection to optional, external EEPROM.
P29 - I2C SDA connection to optional, external EEPROM.
P30 - Serial Tx to host.
P31 - Serial Rx from host.

@Rayman: it's time to upgrade your manual. You are using the first release. Both the datasheet (V1.2) and the manual (V1.1) states 40mA as max io current and 300mA as max supply current. None of them has written nothing about the 100mA max group current (this was only in the old manual v1.01).

Perhaps the first revision was more conservative because Parallax was missing some tests/characterizations

Propeller Object Exchange (last Publications / Updates); Vaati's custom search

Rayman
Registered Member

Date Joined Jul 2007
Total Posts : 2408

Posted 11/2/2009 12:58 PM (GMT -8)

You're right... They did remove that limitation in the new manual...

I'm going to try and sink 100 mA on 8 pins for 800 mA total and see what happens...

My Prop Info&Apps: http://www.rayslogic.com/propeller/propeller.htm

dMajo
Italy 72

Date Joined Apr 2008
Total Posts : 329

Posted 11/3/2009 5:40 AM (GMT -8)

Rayman said...
You're right... They did remove that limitation in the new manual...

I'm going to try and sink 100 mA on 8 pins for 800 mA total and see what happens...

STOP IMMEDIATELY: you have still the 300mA max current limit on the power supply lines. You can sink up to max 40 mA per IO but the total current consumption (including the prop own) should not exceed the 300mA limit.

Some considerations can apply here:

Total power dissipation 1 W

Max. current out of Vss pins 300 mA

Max. current into Vdd pins 300 mA

Max. DC current into an input pin with internal protection diode forward biased ±500 μA

Max. allowable current per I/O pin 40 mA

From current consumption graph (datasheet V1.2 Ch.9.1) we now that @80MHz 8 cogs running spin (so accessing hub - most of the hardware powered) consume 80mA. Still 220 mA are available to both the Vss and Vdd
Now the only current flowing into vdd and out from vss at the same time is the prop internal current consumption. When the output sink current it is flowing into the output and out from Vss, when output source current it is flowing into Vdd and out from the output
Does it means that we can have at the same time 11 outputs sinking 20mA and 11 outputs sourcing 20mA ??? So 20mA on 22 outputs?

Answer: YES. You must pay attention on how you distribute the current arround the IOs and understand the difference between sink (eg. P1 led wired to vcc - ON on 0) and source (eg. P2 led wired to gnd - ON on 1)

Propeller Object Exchange (last Publications / Updates); Vaati's custom search

Rayman
Registered Member

Date Joined Jul 2007
Total Posts : 2408

Posted 11/3/2009 12:05 PM (GMT -8)

Sorry, can't stop! :)

It's worth $7 to see if I can simplify the design...

My Prop Info&Apps: http://www.rayslogic.com/propeller/propeller.htm

Clock Loop
Registered Member

Date Joined Jun 2005
Total Posts : 563

Posted 11/3/2009 12:46 PM (GMT -8)

Rayman said...
Sorry, can't stop! :)

It's worth $7 to see if I can simplify the design...

At least put a heat sink on it, and try to alternate the turn on so that only 4 I/O are on at a time.

Dennis B. Page
Registered Member

Date Joined Sep 2004
Total Posts : 40

Posted 11/3/2009 1:19 PM (GMT -8)

For higher power applications, I like to use the ULN2803A Darlington Array

(http://www.parallax.com/Store/Components/IntegratedCircuits/InterfacingChips/tabid/613/CategoryID/78/List/0/SortField/0/Level/a/ProductID/211/Default.aspx)

and a separate power supply. For lots of outputs, I use the DC-16 Output Expander from ESX-TEK (http://efx-tek.com/topics/dc-16.html).

Dennis B. Page

Rayman
Registered Member

Date Joined Jul 2007
Total Posts : 2408

Posted 11/3/2009 1:46 PM (GMT -8)

Yep, the ULN2803A is my current fall-back plan...

This thing has a lot of LEDs... 64 each of RGB... Ideally, I'd like to drive each at their continuous limit of 20 mA. But, is about 4 A total, so probably won't do that...

Instead, want to drive each at their pulsed limit of ~100 mA at 1/8 duty cycle. That's only 12 mA, but not too bad. But, even I don't think it's a good idea to drive 24 pins at 100 mA. So, I'll do it in groups of 3 for 1/24 duty cycle. This sacrafices brightness a lot, but keeps to total current to more easily manageable levels...

My Prop Info&Apps: http://www.rayslogic.com/propeller/propeller.htm

Post Edited (Rayman) : 11/3/2009 9:54:55 PM GMT

BigFoot
Registered Member

Date Joined Jun 2009
Total Posts : 35

Posted 11/3/2009 6:12 PM (GMT -8)

You might be able to find a small water cooled heat sink for the propeller chip. Then all you would need is a big
pump and a radiator to cool the water.

Russ

dMajo
Italy 72

Date Joined Apr 2008
Total Posts : 329

Posted 11/6/2009 9:25 AM (GMT -8)

@Rayman
If the leds are rgb they are probably common anode/cathode. Try, if you can, to have both of them: common anode and common cathode. Doing this way you can load equally the vdd and vss pins

PEdit: corrected some spelling (PhiPi: this is your job ... did you forget?)

Propeller Object Exchange (last Publications / Updates); Vaati's custom search

Post Edited (dMajo) : 11/6/2009 5:51:10 PM GMT

Toby Seckshund
Registered Member

Date Joined Mar 2009
Total Posts : 477

Posted 11/6/2009 11:53 AM (GMT -8)

At least try to keep the input voltage to the Prop below 9 Volts. They get all "huffy" and won't talk to you again.

Yes it did get hot, yes the EEPROM came out, in solidarity, with it. Yes Farnell had no replacements.

Style and grace : Nil point

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