Heathkit ET-3300 Power Distribution Board & Accessories

Description

Power Distribution Board and Accessories for the Heathkit ET-3300 Powered Breadboard
(ET-3300 Not Included)
This is a unique set of add-ons for the Heathkit ET-3300 Laboratory Breadboard. I built these to help me work on electronics projects using the ET-3300; you won't find them for sale anywhere else. There's a small number of these and when they're gone, I make no promises about making more.
Power Distribution Board:
First up is the Power Distribution Board. Normally, with an ET-3300, you have a mess of wires carrying power and ground from the power strips to the power buses. The power buses don't have red and blue stripes on them, so it's easy to forget whether you've wired power to the left side or the right side. If you're using different voltages on different buses, it's easy to forget that set-up too. If you need a voltage other than the +5V, +12V or -12V the ET-3300 provides, it's messy to wire up an external supply and connect the ground levels. Finally, if you want a ground or power connection for your voltmeter or oscilloscope, you need an extra wire sticking up from a power strip or bus.
The power distribution board solves all these problems. It's a big printed circuit board that plugs into the power strips and buses. It has a 3.3V, 850 mA regulator on board (fed by the +5V supply) and banana jacks for connecting an external power supply. You can then route any of the voltages to any of the power buses just by moving a jumper. The jumper block, with its labeled voltages and bright red shunt, lets you easily see which voltage is on which bus. Your voltage choices for each power bus are +12, -12, +5, +3.3, and External. The shunt has a grip on it - a little plastic tab - so it's easy to grab it and pull it off the jumper block.
There is also a 10uF ceramic capacitor for each power bus to help stabilize the voltage (it's a surface mount cap discretely positioned on the underside of the board).
The left banana plug is red and the right is black. This reminds you that on the power buses, the Power Distribution Board has put power (red) on the left and ground (black) on the right.
Accessories:
Wiring up buttons and LED indicators can be a pain and add chaos to your layout. One side of a button or LED usually goes to the power or ground side of a power bus. The LED can't be wired directly to a microcontroller pin because you need a current-limiting resistor, so that adds more messy wiring. Buttons are hard to wire up because the power buses on the ET-3300 are a weird distance from the component breadboards. The accessory boards solve these problems.
Included in your purchase are five tactile button boards, and five LED indicator boards. These boards are all sized to span the gap between the component breadboard and the power bus. You can plug them into either the power or ground side of the power bus, and they'll reach to the component breadboard area. The LED boards have a 220 ohm current-limiting resistor installed so you can safely drive it from 3V or 5V. The schematic symbol on the LED board tells you which way to orient it for positive logic or inverse logic.
Aesthetics:
In addition to cleaning up a whole bunch of messy wires, the boards all have a blue solder mask that approximates the color of the older Heathkit ET-3300s. To those of you with newer, off-white ET-3300s, I apologize for the color clash. Rest assured, however, that the boards will still work with your ET-3300s; the distances between power strips, power buses, and component areas are the same in the blue and white ET-3300s.
Disclaimers:
First and foremost, this set of accessories is not designed, manufactured, sold or endorsed by Heathkit!
Secondly, the ET-3300 Laboratory Breadboard is not part of this sale. You should either own one already, or be planning to buy one. They're no longer manufactured, but there's almost always a few for sale on eBay. I, for one, highly recommend the ET-3300: it has lots of breadboard area, a built-in three-voltage power supply, and more geek cred than any modern breadboard can provide.