Is there a power pin on STK500?

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Hey all,

I'm in the process of testing a bit with the STK500 and
I'm wondering if there are any power pins that I could
use to connect external hardware..

At the moment I'm in need of 5V for a LCD screen and
I cant seem to find any direct 5V pins to use, like
the GND pins that are available.

Are there any available or will I have to connect
another power supply running on 5V and connect it
to the circuit as well?

If so, will I have to connect the GND lines from the STK500
and the new power supply?

thanks in advance =)
// Chris

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On each port connector, there is VCC and ground.

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oh crap, am I that ignorant.. =O
so, VTG is VCC then?

thanks for the info! =)

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NO! Vcc on STK500 has a current limit, which I don't know, but I'm under the impression it will be too low to power a LCD. Or at least I wouldn't take the risk for a 0.25$ regulator.

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I was looking at that just the other day, when I wanted to use the STK500 as a "lithium cell" for an ATTiny85 to balance. Being able to change VTARGET is useful for that!

Anyhow, it is supplied by a bullet proof LM317M with half-amp current limiting. All current goes through the leftmost VTARGET jumper, so the upper pin of that or better the case of the LM317 itself is where to extract any real current.

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Quote:
NO! Vcc on STK500 has a current limit, which I don't know, but I'm under the impression it will be too low to power a LCD.

I hook it up to a LCD all the time. No problem at all.

From the STK500 manual:

Quote:
Using the on-board supply voltage, approximately 0.5A can be delivered to the target section.

An LCD uses much less than that, typically a few mA. Using the backlight might come close though.

Regards,
Steve A.

The Board helps those that help themselves.

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Chris,

The schematic for the STK500 is available on line. If you have AVR Studio 4 loaded, under the Help tab, AVR Tools User Guide, STK500, Schematic, you can view a PDF of the entire circuit. Page 4 of 9 is the power supply.

If you are using a 5 V LCD you could tap directly off the 78M05. If you are using a 3 V LCD then you could tap off the LM317, WITH VTG SET to 3 V.

Note that the LCD itself will draw very little current, it is the BACKLIGHT for the LCD that is very power hungry.

Perhaps overkill, but if you have a breadboard adjacient the STK500 for your LCD and circuitry, why not just put your own voltage regualtor on the breadboard. This is a much better option than either of the above.

If you want to power it off of the same wall wart powering the STK500, then tap your power off of the Bridge Rectifier, D601, which sits between the STK's barrel power supply connector, and the RS-232 connector.. In this way the same wall wart and single (STK) power switch can be used. Bring both "VIN" (from the bridge), and Gnd over to your breadboard and your own voltage regulator.

If you chose to use a totally separate wall wart, and voltage regulator, which is also a fine aproach, be sure to tie the Ground from the STK to the Ground of your additional power supply. Do NOT tie their V+'s together.

If you are using a regulated wall wart to power the STK, then one more option is to power the LCD's LED backlight from the STK "VIN", (from the bridge rectifier), and power the LCD itself from the STK's own power bus, 5V, or VTG. You would select a series resistor based upon the VIN voltage, which depends upon the wall wart's voltage.

JC

Edit Typo, and beaten by Steve...

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This photo shows tapping off the bridge rectifier.
The Black/Green & Blue wires go to a 78L05 power supply in the upper corner of the breadboard. STK doesn't overheat. One switch for everything. Easy.

JC

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Quote:

it will be too low to power a LCD.

Just how much current do your LCDs take?

I always thought mine took next to nothing. Now backlights might be a different matter, but I'm hard pressed to think of one > ~200mA.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Quote:
The Black/Green & Blue wires go to a 78L05 power supply in the upper corner of the breadboard. STK doesn't overheat. One switch for everything. Easy.

Take the power directly from one of the readily available headers - even easier. I can't believe that you would recommend soldering wires onto the STK500 just to power a 6mA LCD.

Regards,
Steve A.

The Board helps those that help themselves.

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Quote:
are any power pins that I could
use to connect external hardware..

Yes and No...

I have some very low power LCDs, some with very low current LED backlights. But it is not a given that the OP will have one of these.

I also have some (old) LCDs that draw over 200 mA for their backlight, (some well over 200 mA!).

The OP mentions, first, "external hardware". Not a highly specific specification... Probably because they do not themself yet know exactly what they will be connecting.

If, next week the OP adds a 50mA GPS and a 40 mA XBee/Bluetooth module, and a GLCD, and an SD card, ....

Time to quit when the RED led dims, or you can fry an egg on the voltage regulator. :)

Steve's solution is quick and easy, and is in spec for low power add ons. My suggestion is perhaps more robust, and your peripherals will not be subject to whatever you happen to set VTG to at the moment.

JC

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wow thanks for all the response =)

well the reason I asked was because I couldnt find any direct 5V named
header on the board and instead of tapping into the "power supply" part by modifying the
board as it has been very nicely explained here on how to do, I thought of asking first
as it might have been thought of by Atmel when they made the board..

but apparently it seems that we're not supposed to connect too much into the board itself ;)

anyway, my solution for this will most probably be to power the "controller" board that
I've made for the LCD (with the pot and conversion into a 10-pin connector and so) with another
wall wart and a separate 7805 for the LCD.

so connecting the GND wire of the new wall wart to the GND pin of the 10-pin connector
to for example the PORTA connector would be enough?

then I could power all the +5V necessary for the LCD (+5V LCD, LED backlight and so on)
with the new wall wart and I won't stress the STK500 wall wart at all and it shouldnt be
any problem with noise or something like that with two separate power sources with a
combined GND connection?

just as a note, I had successfully connected the LCD to the 10 pin PORTA header with
both the LCD and the LED backlight functioning on the STK500, so just a note that it does
work but perhaps we shouldn't connect much more than that ;)

but it also was just for a short bit, 5 min or so, while watching and crying happy tears
that I just got it to function before I went to work =)

so while I really love the explanations on how to tap into the STK500 without header pins
I think I'll skip on that as I probably still have warranty left on the board ;)

also this thread might be useful for others in the future, I hope! =)

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Yes, using a separate power supply will work fine.
Yes, tie the Grounds from the two boards together.

Good luck with your project!

JC