PBB 272

The PBB 272 is a powered breadboard. Currently, there are 20 of these in B209 Fitzpatrick for use with EGR 119 and ECE 141.

PBB 272

Specifications

The following list taken from Circuit Specialists

• 5 Distribution Strips (500 tie points)
• 3 Terminal Strips (1890 tie points)
• 4 Binding Posts
• One Ground
• One 5VDC (1 AMP) Constant Power
• One 0 to +15VDC (500mA) Variable Power
• One 0 to -15VDC (500mA) Variable Power
• 110VAC Input Power, ± 10%

Connections

Ground and Voltage Posts and Settings

PBB 272 Ground and Voltage Connections

PBB 272 As Typically Wired

The PBB 272 has a ground connection and three different voltage sources - a 1-Amp capable +5 V source, a 0.5-Amp capable positive source adjustable between 0 V and +15 V, and a 0.5-Amp capable negative source adjustable between 0 V and -15 V. The adjustments for the latter two are made using dials located just under the sources themselves. Note that for accurate voltage settings, some form of voltage meter must be used since the PBB 272 themselves do not have a readout for the voltages.

While the binding posts for these four voltages have thumbscrew that can be used to firmly attach lead wires, experience has shown that the conducting material in the thumbscrew cracks easily leading to a bad connection. Instead, four colored alligator clips are typically used in concert with jumper wires to connect the binding posts to the breadboards. The second picture at right shows the typical color configuration:

• Black: ground
• White: +5 V
• Red: Adjustable 0 - +15 V
• Yellow: Adjustable 0 - -15 V

Breadboards

There are a total of eight different breadboards on the PBB 272 - 5 distribution strips and 3 terminal strips.

Distribution Strips

The distribution strips are the thin boards that have a blue strips on one side and a red stripe on the other. On an single distribution strip, all pins on the blue side are connected together and all pins on the red side are connected together. Note, however, that red and blue are not connected and also that red on one strip is not connected to red on any other strip. The distribution strips therefore provide 10 independent sets of 50 pins each. These are primarily used for ground, voltage sources, or common points within circuits.

Terminal Strips

The terminal strips are the wider breadboards running vertically in the center of the PBB 272. The rows of these are numbered every 5 rows and each column is labeled. On these boards, groups of five pins in half-rows are connected together. For example, at the top left of the left terminal strip, pins F63, G63, H64, I63, and J63 are connected together. They are not connected to A-E63 in that terminal strip, nor are they connected to F-J63 on either of the two other terminal strips. This means there are 378 (63 rows per column * 2 columns per board * 3 terminal boards)independent groups of 5 pins each. These are useful for making connections within a circuit that require between 2 and 5 total connections. If more are needed, groups can be connected by a "jumper" (basically, a wire) that will link a total of ten pins together.

Pin Addressing

The PBB 272's in B209 have an "interesting feature" - the boards were seemingly installed upside-down such that "row 1" is on the bottom and "column A" is at the far right of a board. Unfortunately, it requires removing on the order of 24 machine-tightened screws to reorient the breadboards so...they have remained upside-down.

For the distribution strips, pin addresses are generally given first as a combination of which color and which distribution strip to use. To determine which strip, the top one is called "top" which the other four are numbered 1-4 from left to right. For location, a general area to connect a wire is needed. As an example, Blue 2-21 means to use the blue side of the second vertical distribution strip and specifically a pin location close to the 21st row (using the numbers from the nearest terminal strip). Since all the blue pins in a column are connected, distribution strip rows do not need to be exact.

For the terminal strips, pin addresses are generally given first as an indicator of which column to use (numbered 1-6 going left to right), followed by a lettered column and a numbered row. As an example, Col 4-E20 would be in the fourth half-row in the E column and the 20th row. As a point of reference, this particular E column is a little to the right of the ground plug at the top of the PBB 272.

Use

Turning On

When turning on the PBB 272, if you have any circuits connected to any voltages make sure there are no circuit elements that will react poorly to a step change in voltage. This is especially true of anything connected to the +5 V source since it cannot be gently ramped up from 0 to +5 V. Make sure both adjustable sources are turned all the way down, check to make sure there are no loose connections or stray wires, then turn on the master power switch. You may then make any voltage adjustments for the +15 V and -15 V sources - typically setting the +15 V source first then setting the -15 V source. As always, for precision settings, use the multimeter to read the actual source voltage while turning the dial.

Turning Off

To turn off the PBB 272, follow the opposite procedure. First, turn the -15 V source all the way to 0, then turn the +15 V source all the way to 0, and finally turn off the master power switch. Unless there is some overriding engineering requirement, the adjustable sources should always be turned full counter-clockwise when toggling the master power switch.

Questions

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