View Full Version : Vin vs. Vdd

11-17-2009, 06:19 AM
Dear Forum,
I've a BS2e and I'd want to know what is the better configuration for give electrical supply to my BS2e.
I'm confused because I don't know if I have to use VIN pin and then the regulator on board or otherwise I have to use VDD e VSS whit an external regulator.
Please help me because this important issue is not specified.

Greeting from Italy

Post Edited By Moderator (Joshua Donelson (Parallax)) : 11/16/2009 11:31:39 PM GMT

11-17-2009, 06:24 AM

You could either power the BASIC Stamp from either the Vin & Vss or Vdd and Vss, but not using both. If you power the BASIC Stamp using Vin, it will use the on-board regulator to regulate the power down to 5VDC (which is safe for the BS2). The other way you can power the BASIC Stamp modules, is·apply power the Vdd with a steady 5 VDC. This will power the BASIC Stamp via the output of the regulator Vin uses. Just be sure to either power via the Vdd or Vin, but not both.

Thank you and I hope this helps,


Joshua Donelson
www.parallax.com (http://www.parallax.com)

Post Edited (Joshua Donelson (Parallax)) : 11/16/2009 11:31:58 PM GMT

11-17-2009, 03:24 PM
Dear Joshua,
I want to thank you for your important response.
I know that the regulator on board can burn very easy if I use more LEDs for example or more output that draw in high current.
What do you think is the better use? Use the internal regulator or external?
Where I can find this issues? Manual? PDF?

Thank you very much


11-17-2009, 11:43 PM
The on-board BOE regulator (an LM2940 I believe, or an LM7805) should be good to 1.5 amps, which is a LOT of current for a small board.

There's another regulator on the BS2 module itself, which is only good to 50 mA.

So are you using the BOE board? It's not clear which regulator you're talking abou.

11-18-2009, 12:14 AM

I generally use an external regulator rather than the one on the BASIC Stamp because of the output difference like Allenlane5 explained. There are various ways to supply voltages, so I don’t know if there is going to be a diagram. Depending on the amount of LED's you want to use for your project, would determine if you needed a separate supply. What would you like your project to do?


Joshua Donelson
www.parallax.com (http://www.parallax.com)

11-18-2009, 03:26 AM
Thansk to all for the useful response,
I've not a BOE but a simple BS2e module with a carry board.
If I place my BS2 on carry board (www.parallax.com/Store/Microcontrollers/BASICStampDevelopmentBoards/tabid/137/List/1/ProductID/121/Default.aspx?SortField=ISBN%2cISBN (http://www.parallax.com/Store/Microcontrollers/BASICStampDevelopmentBoards/tabid/137/List/1/ProductID/121/Default.aspx?SortField=ISBN%2cISBN)) , I'm forced to use the regulator on board?
I' want to realize a rover with four servo motor, two for wheels and the other two for the pan and tilt of a web cam mounted on board.
Next, I want to connect this rover to my PC trough, I think, a FOX BOARD module and send a command to BS2.
Now It's more clear?

Thank's a lot

Daniele from Italy

11-18-2009, 03:54 AM

That board doesn't have a external regulator; so if you used the Vdd on that board it would be limited to the 50mA coming off the BS2. What you can do, and what I would suggest, is adding an additional regulator on that board to power the servos. Keep in mind, that the power supply coming from that board is a 9V battery which do not have an exceptionally long battery life, especially when running servos. In that case, you may want to get a separate power supply·for the additional regulator to power the servos or anything requiring more than 50mA;·just be sure to connect the common ground. For example, using a battery pack for your motors and the 9V for the circuits.


Joshua Donelson
www.parallax.com (http://www.parallax.com)

11-18-2009, 03:59 AM
Ah, that's much more clear.

The Super Carrier Board: http://www.parallax.com/Store/Microcontrollers/BASICStampDevelopmentBoards/tabid/137/CategoryID/12/List/0/SortField/0/Level/a/ProductID/122/Default.aspx
$19 -- has an on-board regulator which is good to 1.5 amps.

Yes, what you have IS the simple carry board, which does not have an on-board regulator, so you'd be using the on-module regulator, which simply can't provide enough power for all you want to do. You COULD add your own regulator and a couple of capacitors to the carry board -- look up LM2940, or LM7805 on google for more information on the simple circuit needed to use these.

11-18-2009, 04:07 AM
Absolutely, you could instead get a Super Carrier Board;·the extra circuitry I was explained earlier would be included.·As long as you didn't exceed the current limitations of the super carrier board, it·should work without alterations. For the cost, the Super Carrier might be an easier than adding the addional hardware.


Joshua Donelson
www.parallax.com (http://www.parallax.com)

11-18-2009, 04:21 AM
DOH! allanlane5 http://forums.parallax.com/images/smilies/cool.gif
I' ve buyed the other carry board...cheaper :(

Ok, don't worry guy.... Now, can you see If I wrong?

I put my BS2e on carry board. Then, to avoid to use the on-module regulator, I use an external regulator like 78l05. Then, I not use the VIN input but only the VDD and VSS BS2' pins. In this way I can't use the 9 V battery supply on the carry board, right? I've to use an external supply for the BS2 module passing trough my 78l05.
Then, I use another supply (6 Volt ) for my 4 servos and I pay attention to connect common ground.
It' s right?

Thank you very much for all response

PS: Now I go to sleep 'cause here, in Italy, is 10:20 PM http://forums.parallax.com/images/smilies/burger.gif
Guys, If you can, leave here your suggestion and response, I read it tomorrow, whereas you sleepping http://forums.parallax.com/images/smilies/hop.gif

11-18-2009, 04:36 AM
The 78L05 only puts out 100 mA, which isn't going to drive 4 servos.

Now, if you use 4 1.5 volt AA alkaline batteries, or 5 1.2 volt AA NiMh batteries (making 6 volts), you could tie their output directly to the V+ of your servos. You could also tie that to the Vin of your BS2. Then connect your 'common grounds'. Then the signal pins from the BS2 will be able to drive the signal pins of your servos -- the signal pin of a servo doesn't take very much current at all. Or you could drive your BS2 with the 9-volt battery, and the servos with the 6-volts.

This leaves the power to drive your web-cam -- which might take a 78L05, or simply it's own 9-volt, I don't know what your web-cam needs.

Things you should not do:
1. Don't drive your servo's with more than 7.5 volts, it will damage them.
2. Don't try to do too much with a 9-volt battery. They only put out about 50 mA, where your servo's will need 300 mA each or more.

Having said all this, it seems to me I've just repeated most of what you already said, so I think you've got a good handle on what will work.

11-24-2009, 05:10 AM
Hey Guy,
I've more clear idea about my project.
Now, I have to use 4 servos and one SFR04 (ultrasounds).
Please correct me If I wrong.
I've a cheaper board in which I put my BS2.
Now, I'd want use 9 v battery for BS2 using VIN pin and then regulator on board.
Another supply for servo trough 6 volt battery.
I run some risk using on board regulator? I think no, because I want use only signals pin; 4 for servos, one for SFR04 and another one for LED.


Post Edited (sonique) : 11/23/2009 10:37:07 PM GMT

12-03-2009, 12:33 AM
Hey Boy,
I'm very happy about my BS2. =)
I decided to set up an external circuit with 7805 (1 A current). Now I'm trying to use my four servo with PWM signal.
Thank you so much