BS2P40's with different current draw

T Chap

Stamp1 has a blown pin 2 but otherwise works fine
Stamp2 has no known functional problems
Stamp3 "

My board pulls 100 mA when no Stamp is inserted. When I put the same program in each Stamp and read the current to the board I get the following:

1 = 270mA (dead pin2)
2 = 200mA
3 = 150mA

My assumption is Stamps 1 and 2 are damaged but still working somewhat. The data sheet says 40mA is normal when running, so 3 is fine. What can be wrong with 2 if I can't detect a problem?

RobotWorkshop

Do all the Stamp modules have the exact same program in each one?? If not they could be driving the pins differently or using more/less features of the Stamp itself.

If you want to fix your module with the blown pin 2 you can buy their OEM chip and replace it. Not the easiest job in the world but I just did one since I thought the original one was dead. To get the old chip off I used a fine point exacto blade and lifted each pin as I warmed it with the soldering iron. Once the chip was off Solderwick was able to clear off the exess solder on the pads. The new chip was carefully placed and soldered on a couple pins (47 and 48 since they are together anyhow) and then adjusted until it lined up perfectly. If you have all the fancy surface mount gear (I don't) I suppose it would be easier. To solder on the new chip there are a couple techniques i've used with good results. The first is just go ahead and solder a whole side at a time without worrying about solder bridges. Once each side is cool then go onto the next. Once done you can go back over each side with the solder wick to remove the solder bridges and excess solder. The results are better than you might think! Just let it cool after doing each side. The other method (after the first pins are tacked in place and the chip is adjusted) is to use a couple drops of liquid flux on each edge of the chip to get on the pins and the pads. If you then put a little solder on the tip of your iron you can lightly draw it past each pin and pad and with the extra flux it usually makes a perfect solder joint. If you happen to get a solder bridge just use the solder wick to fix it! If you deflux it once done it is sometimes hard to tell if you did it or the machines.

Best Regards,

Robert

Kirk Fraser

I have a BS2P40 but unfortunately I soldered directly to the pins instead of chopping up enough IC sockets to handle all the pins. Have you been using sockets or direct solder? Sockets sometimes have problems -- on one TLC2543 I had trouble with a socket on only one pin and I couldn't get it working with a soldering iron so I had to trash the board with the defective socket leg. I suppose a micro-short could cause a little more current draw. Or overuse could cause wear on resistive circuitry or degrading of capacitors causing a little more draw. In my opinion, it's something to live with, unless you can't.

Chris Savage

Wasn't there already a thread on this subject?· The BS2p40 draws 40 mA not including anything connected to the I/O or drawn from other sources from the P/S.· Given that, if you're reading that much current draw I would guess there is something wrong with your meter.· You can easily find out and test the meter by connecting an LED up to power through a known resistor and testing the current draw.· You will need to know the specifications for the LED as well (V_FWD).· Knowing this information it would be easy to calculate the current draw and measure it.· For example and LED with a forward voltage of 1.4V and a 220 ohm series resistor should draw around 16 mA.· Test something like that with your meter and see what you get.· That may help identify the source of the current draw (meter or circuit).

P.S.- To test the current connect the cathode of the LED to GND.· The anode should go through a 220 ohm resistor to the black lead of your meter.· the red lead should go to 5V (Vdd).· The meter should be set for DC current at the closest sclae to 20 mA without going over.· I hope this helps.· Take care.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

T Chap

Chris not sure how you misunderstood my info:

My PCB that has other circuitry WITHOUT the Stamp pulls 100mA. When I plug in a good Stamp, the PCB then pulls near 150mA. There are two other suspect Stamps that cause the board to pull the variants mentioned above. I was only questioning how the Stamp could still function properly and have an obvious internal problem, since two are pulling a lot more current that the known good one. The math I just suggested will give you around 40mA for the good Stamp, 90mA for another and 170mA for the other. I don't have a problem testing current.

These values include my entire PCB with numerous other components on it, plus the Stamp:

1 = 270mA (dead pin2) Works fine but blown pin 2, but pulls a lot of current
2 = 200mA This Stamp works fine, but draws more
3 = 150mA Good Stamp

RobotWorkshop

Hello,

Have you checked to see if all the BS2p40 modules you have are the same revision? When you use the Identify routine do they all respond the same?? Perhaps if they are different versions or have different components on each module that would account for the difference in current draw. They either always had a difference in current consumption or something changed to make one draw more than the other.

I did go back and see that you are downloading the same program in each one so that should not be the problem. Another thought (which perhaps the folks at Parallax can confirm/deny) is if the settings for the pins (inputs or outputs) are persistant and stored in EEPROM so that they would only change when specifically told to do so by the downloaded code. I suppose adding a few lines of code up front to specifically define each pin before downloading it to each stamp would rule that out. I don't think it does remember the pin settings (direction) after being powered off but getting confirmation would be good.

Best Regards,

Robert

Amaral

Originator , just to be sure , can you measure the stamp alone ? with no cone on it ! that would simplify many variables that you may be triggering with the stamp in a board full of stuff.


Amaral.

T Chap

It's too much hassle to pull the Stamps power pin out of the socket and run in a wire back into the socket to insert the meter for the Stamps current only. The Stamps are all brand new, but like I said I think two are damaged somehow, one for sure has a blown pin2 which I can switch out, but it draws 170mA alone. It's no big deal really, they are just out of stock and I needed some today and was looking to salvage these maybe. I'll just deal with the damaged goods until they get in the new ones. Thanks folks for the effort anyways. Todd

Chris Savage

Amaral,

·· You make a good case, and in this sense there's no real way to know without removing all the unknown variables.· These "bad Stamps" could be triggering circuits on the board which are drawing the extra current.· Bottom line, the only accurate way to measure the current draw of the Stamp Module is to do it out of circuit.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

Tracy Allen

Be sure all Stamp BS2p40 pins have pullup/down resistors or that they are initialized as outputs. If that is not done, the apparent current consumption of different Stamp chips placed in the same circuit board can vary widely. That is because some chips will come up with pins floating right at the switching threshold and that causes the chip to draw excess current.

You should be able to put any Stamp in that board and figure out the proper initialization state of all 32 pins, so that when the Stamp is in _SLEEP_, the circuit draws exactly the same current as it does without the Stamp present. And when it wakes up from SLEEP, the current is consistently ~40 ma more.

If you draw a finger across the Stamp pins, and you see the current change widely, that probably means you have uncontrolled floating input(s).

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Tracy Allen
www.emesystems.com

T Chap

Tracy Thanks for the tip. All unused pins are set to outs. These chips are surely damaged by serious abuse in prototyping (shorts etc). I'll check out the sleep test though. I don't have much time to deal with it, I'll just wait till more come in. I am making new boards that will use the Propeller anyways, so this is just to finish out a last batch of Stamp boards before obsoleting the Stamp. They served their purpose for a while though getting my feet wet.