# Power Supplies

Parallax BASIC Stamp Development Boards may have either a barrel jack connector, 9 V battery clip connector, or both (as does the Board of Education.) This page gives options for both types of power connectors.

## For Boards with a Barrel Jack Connector

The two most common power supply options used with this connector are wall-mount DC power supply, and battery holders.

### Wall-mount DC Power Supplies

- Plug: it must have a 2.1 mm center-positive barrel plug. Look for this symbol, indicating the positive connection is in the center of the plug:

- Output current: wall-mount power supplies must have a DC (direct current) output. Look for a statement that indicates VDC output or uses this symbol: . For example:

- OUTPUT: 7.5 VDC 1000 mA
- OUTPUT: 7.5 V 1.4 A

- Output voltage: The power supply's output voltage must be compatible with the voltage rating on your board. For example, the Board of Education requires 6 to 9 VDC.
- Input voltage and current: Wall-mount power supplies must be compatible with the frequency and amplitude of the AC power at the wall outlet you are using. This may vary depending on the country you live in. In the US and Canada, the input should be compatible with 120 VAC, 60 Hz.

Parallax carries power supplies compatible with BASIC Stamp development boards. For example, the 7.5 V, 1 amp supply (#750-00009) is compatible with the Board of Education.

### Battery Holders

Like wall-mount supplies, battery holders must have a 2.1 mm center-positive plug. However, many battery holders don't have a symbol indicating whether or not the plug is center-positive. Use a voltmeter to test any battery holder of unknown origins. A 4 AA cell battery holder with a 2.1 mm center-positive plug is available from Parallax (#700-00038); this is the one included in the Boe-Bot Robot Kit.

## For Boards with Battery Clip Connector

### 9-Volt Batteries

9 V Alkaline or rechargeable batteries with a snap-connector are fine. For best results, rechargeable batteries should be rated for 100 mAh (milliamp hours) or higher.

Not all chargers work with all types of batteries. Make sure your charger is recommended for the type of battery you are using. Follow all battery and charger instructions and caution statements.

### 9 V Battery Extension

The figure below shows a DC supply and a 9 V battery extension that can be used with battery clip connectors, such as the one on the BASIC Stamp HomeWork Board. Read the CAUTION statement below the picture.

### Beware of Universal Adapters and Reversed Supply Terminals!

The picture below shows a common mistake that should be avoided with universal adapters. Many of these allow you to reverse the terminals on the 9 V battery extension. Although it cannot hurt the BASIC Stamp, Board of Education, or HomeWork Board, it can destroy a Parallax Standard Servo connected to Vin in a matter of seconds. The only system that can protect the servo from this mistake is a Board of Education that has a jumper between the servo ports, with that jumper set to Vdd.

### Beware of "Battery Replacers"

Many battery replacers are designed to supply appliances with low current draw. With current ratings in the neighborhood of 10 mA, their output capacities are insufficient for many of the activities in the Stamps in Class texts. For example, two LEDs connected to 220-ohm resistors draw a total of 14.5 mA, and that definitely won't work with a "battery replacer."

Note: It's pretty easy to tell when a circuit is drawing more current than the supply can deliver because the Power LED on the Board of Education flickers and/or goes dim. On the HomeWork Board, the "Running" LED may flicker if the power drops low enough to cause the BASIC Stamp to reset and restart the program.

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BASIC Stamp Help Version 2.5.4

Copyright © Parallax Inc.

8/8/2012