View Full Version : Vin and Vdd
02-26-2005, 03:28 AM
Would it interfere with normal operation of any of the Stamps if I cut off pin 24 - Vin?· The output of the Stamp internal regulator is in parallel with Vdd - Pin 21 - on all the Stamp schematics I have looked at.· It occurred to me that if there were any difference in the output of the internal regulator and the external regulator this could cause unwanted current flow and overheating of one of the regulators.· It appears to me that all Stamps would operate normally without Pin 24.· And on BOE Rev A this pin was not connected to anything.
02-26-2005, 03:38 AM
Cutting pins off your BASIC Stamps will void their warranty -- it's best just to leave the pin unconnected like with the BOE Rev A.
Applications Engineer, Parallax
Dallas, TX· USA
02-26-2005, 03:43 AM
Can't do that, Jon.· There is a big trace going to Pin 24 from the external power supply - of course I guess I can just cut that trace.· That won't affect my Stamp warranty.
K de Jong
02-26-2005, 08:53 AM
If you are concerned about building you Piggyback modules you could leave pin 24 unconnected at the top level, that is where your Stamp is. This way your other applications can get their power and leave the Basic Stamp voltage regulator unconnected.
02-26-2005, 09:02 AM
There is no way to do that, Klaus.· One of the modules gets its power from Vin, and the Stamp plugs into the same pin.· Cutting the Stamp pin off was one way to do it, the other is cutting the trace from the external power to Pin 24 - Vin.·
I can solve the piggyback problem by modifying the little PC boards so the piggybacks get their power from Pin 21 - Vdd - instead of Pin 24.· This is a local problem and I'm just trying to keep the BS2P from getting so hot.· I thought removing Vin from Pin 24 might be a start because of possible voltage differences in the internal and external regulators.
What are you doing up so late????
02-26-2005, 09:11 AM
Klaus, I just thought of something else I could do.· I could put an extra set of headers underneath the Samp, cut off pin 24 so the Stamp does not have conact and remove Vin from the Stamp that way.· In fact, that is what I will do in the morning.· Good idea - thanks for the suggestion :))
Tell Lidy you are very smart.http://forums.parallax.com/images/smilies/yeah.gif
K de Jong
02-26-2005, 08:16 PM
If I look at the piggy back I have here it actually has an extra header on top. So it can be done with the one I have here. That is what I had in mind yesterday.
My projects are evolving rapidly. I now use the EB500 Bluetooth adapters and the IR-Buddies for my 'remote datalogging' project and it is amazing how these Parallax pieces work right out of the box. Follow the instructions in the manual, put power on them and off you go http://forums.parallax.com/images/smilies/smile.gif))).
With an IR-Buddy and a TV handset I can program a datalogger in the field without the need of a keyboard on it http://forums.parallax.com/images/smilies/smile.gif.
Success with your 'pin 24' problem,
02-27-2005, 01:05 AM
Klaus, I just made a remarkable discovery - at least to me.· Pin 21 - Vdd - on the Stamp and Vdd on the AppMod header are not connected to the external regulator.· Vdd at the top the the little white breadboard IS connected to the external regulator.· This means that everything I plug into the Stamp socket is running off the Stamp's internal regulator.· No wonder the darn thing gets hot!!
I was considering running a jumper from the Vdd at the top of the breadboard to Vin on the AppMod header to reduce the load on the internal regulator.· I measured the internal regulator voltage at 4.95 and the external regulator voltage at 4.96.· Do you see any problem if I install the proposed jumper.· Alternatively, I could·connect a wire·to the piggyback voltage input and plug it into Vdd at the top of the breadboard.· This is what I had to do with the MCP23016 piggyback.
K de Jong
02-27-2005, 06:38 AM
Interesting, on my BS2p demo Board pin 21 (VDD) apears to be connectod to the 5 Volt output of the external regulator. Pin 24 is not connected to anything, as far as I can measure.
To my opinion the best would be to leave the parts supplyed by Parallax in their orinal state and make the adjustments on your expansion boards. Best would be if you were able make the adjustments in a way that your tiny bourds would fit to as many Parallax boards as possible.
Maybe you have to cut your piggy back system from both pins 24 and 21 and give them a power supply wire to the top af the breadboard.
There seem to be different layouts used in the Parallax boards http://forums.parallax.com/images/smilies/smile.gif.
I hope this helps,
02-27-2005, 11:59 PM
Finally got the Vdd problem cleared up.· Talked to Aristides at Parallax.
On the Rev A BOE Pin 24 - Vin -·is not connected to anything and Pin 21 -
Vdd -· is connected to the external regulator.· On the Rev B BOE Pin 24 is connected to Vin and Pin 21 is not connected to the external regulator.
On the Rev C BOE Pin 24 is connected to Vin and Pin 21 if connected to the external regulator.· I have all three revisions but I use Rev B most of the time.
I ran a jumper from the regulator input on the piggyback to the external Vdd.· This would not be necessary if a person was using the Rev C, but since I never know I wanted to make a board tht was universally compatible.· Had to drill a tiny hole in the piggyback PC, but now the unit is working great, receiving RF data from the shop.· The BS2P24 still runs a bit hot, but not nearly as hot as it was.· I will probably stick with the·BS2E since it always runs cooler.