Mescream

invention

Inline Power Module

by chris101

Published on May 13, 2016

Ever have an invention using a bit that draws a lot of power, like the fan or servo, and the device either runs rough, like it needs a tune-up, or stops working entirely? Or are you running something mechanical in a synth circuit, and you get a buzz in the speaker? If so, the problem may be that your power circuit is creating noise, or over-powering the litleBits power supply.

This invention, the inline power module, provides a way of giving power hungry, or electronically 'noisy' bits their own power supply, which is independent of, and isolated from the main power bit of the circuit.

 

 

Duration: 4 hours if you have soldering skills

Credits: I would like to thank Alex Pikkert ( @alexpikkert on the Forum)for his help and support in the development of this module. @SeventhDarf and @JackANDJude also participated in the development. Thank you all!

How To Make It

1

The problem Occasionally a circuit fails because the power supply is being starved when a bit with a high current draw, such as a servo motor, is added. Normal circuit design says that he new bit needs it's own power supply. On the other hand, littleBits philosophy says the entire chain of bits should be powered by a single power bit at the beginning of the chain.

2

The solution Since circuits may exceed the supply provided, I have gone outside of the standard littleBits library, as well as also extending the philosophy, by using a basic circuit design principle: Provide a separate power supply to bits that may suffer from a depleted or noisy power line.

3

The first prototype The most basic prototype has one power in, a second power out, and a shared signal line. This device can be made with a proto-module and half a wire bit. Hook them up as shown. This version works fine, but does have an occasional spasm, and is more often than not, off by one. NOTE: This simple form of the device can be made from standard off-the-shelf littleBits.
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4

The second prototype (a step to far) In a second prototype I attempted to increase the amount of isolation by using an opto-isolator, however the design was too complex for the need, so I abandoned (for now) this path.
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5

The third prototype (just right!) My third prototype had just the right amount of isolation, and complexity. The isolation comes solely from the op-amp, by virtue of it's high input impedance. Signals cannot travel backward through an op-amp. Here is the fifth prototype, using only an op-amp:
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6

The final prototype A well behaved module in the littleBits world has certain characteristics which are described in the littleBits HDK Manual (or you can look at the schematic of any of the littleBits modules from a link on the bottom of the module's web page.) To incorporate these a few more components are needed, a few resistors, capacitors and a ferrite bead. I had previously made a circuit board with a coping saw and nippers to accommodate three bitSnap connectors. To guide my soldering I made a couple drawings, first a logical layout of the components, to be sure there is enough room, etc. Then a second drawing, flipped left and right, to show the wiring from the bottom. This is my guide while soldering. I soldered the circuit together using standard through-hole components and wire.
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7

How to use it Once all the connections are made, the bitSnap connectors are attached, and the inline power bit is done! The module can be used with any other littleBits modules. The purpose of the module is to supply power to subsequent bits. It is a Wire bit, not a Power bit because a power supply, such as a battery or USB cannot be attached to it directly. Two power modules are needed, to supply power to each of the input connectors. The signal from the second power input is not used (It is pulled high through a 1 mega ohm resistor.) The signal from the input on the left is passed through the op-amp unchanged, to the output connector on the right. Put this module into a circuit directly before a high power drawing bit. I think the servo is the most power-hungry bit, so that is what I have used to test it. Changing the input on the left side of the circuit shown in the video (at the top) smoothly changes the position of the servo, even under a high load, and a weak power supply on the left. For the most power to be available, power the second input (the top connector) with a usb power bit, connected to a wall supply that can deliver more than 1 amp. A loaded servo can draw that much when it changes directions. That's it! The bits after the inline power bit run the same as they would if they were directly connected, but smoother and cooler!
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