PDA

View Full Version : Basic Stamp Add on Board



KenLem
05-04-2006, 09:45 PM
I'm working on an add on board for a Basic stamp. It requires too much power to drive directly from the stamp's regulator so I'll put it's own regulator on the board. My question is what should the max voltage be? I was thinking it should be 9v. Is that right?

What do other people do for regulators on stamp add on boards?

Thanks.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.speechchips.com (http://www.speechchips.com)

Speech & Video IC's for BasicStamps

Chris Savage
05-04-2006, 09:59 PM
The input voltage to the Add On would depend on the rating of its regulator.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

KenLem
05-04-2006, 10:20 PM
Hi Chris,

Right. I didn't phrase that correctly. I want to use the same input voltage as whatever is powering the stamp. What is the max voltage of the regulator on the stamp?

Thanks.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.speechchips.com (http://www.speechchips.com)

Speech & Video IC's for BasicStamps

Chris Savage
05-04-2006, 10:35 PM
That somewhat depends on what is connected. In the case of the Board Of Education we recommend no more than 9V. This is mainly because this board can have servos connected and that is around where the servo could be destroyed. If you're not using servos the recommended max voltage is 12V. You should always verify the output of the supply when using anything over 6V just to be sure what you're using. Some unregulated supplies can put out much more voltage than they're rated at when not at the rated current load.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

Andyh
05-05-2006, 03:15 AM
KenLem -
Remember to connect the externally regulated 5v power to VDD, pin 21 (on the BS2p that I'm using), not to VIN, pin 24. I'm using a LM317 regulator. If you use the LM317 note the regulated output voltage is on the tab, so don't screw it down to a metal case. - Andy -

allanlane5
05-05-2006, 04:40 AM
In the 'olden days' of S100 busses, people used 12 volts (I believe). The max voltage for the on-board regulator is probably around 26 volts -- but you really wouldn't want to go there.

The limiting factor here is how much power (aka heat) the regulator can dissapate before it over-heats. Now, Power is Voltage Times Current (P = IV). Say you're putting 9 volts across the regulator. It has to drop 4 volts, to get your nice fixed 5 volt output. Now, if you pull 1 amp through your regulator, 1 Amp * 4 Volts == 4 Watts, which is a lot, but doable.

If you're using a 12 volt supply, supplying that same 1 amp at 5 volts requires dropping 7 volts across the regulator. Now you're at 7 watts -- I think the practical limit is 5 watts, but you can look up the LM7805 docs to see for sure. Also note all that heat is 'wasted' power -- which you may not care about if powered from a wall-wart, or could be a big deal if battery powered.

Bottom line -- 7.5 or 9 volts are very nice values to start with. Note also the LM7805 requires at least 1.5 volts across it for it to regulate -- any lower than that, and your output voltage drops. Note also the LM3840-5 is a "low-drop-out" regulator, which only requires like 0.5 volts across it to regulate. But it costs $3.00 versus $1.50 or so for the LM7805.

stamptrol
05-05-2006, 07:28 AM
If its for a commercial or industrial project, one of the most built-proof ways to power the Stamp and any add-on stuff is with a mini switching regulator. I've used hundreds of PT5101N switchers ( DigiKey) on my controller boards. They deliver 1A with no extra heat sinking, handle any input voltage from about 8volts out to 30 volts. The only extra component required is a small 100uF cap on the 5v output. You will find the price high if this is a hobby project; about $15.

KenLem
05-05-2006, 09:32 PM
Thanks for the all the responses.

Stamptrol - The PT5101N sounds useful but is far too expensive for what I'm doing.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.speechchips.com (http://www.speechchips.com)

Speech & Video IC's for BasicStamps