Cheap power supplies

Introduction

This post lists some cheap options for power supplies to use in electronic and embedded systems projects. We will cover try categories: breadboard power supplies, AC-DC adapters and batteries.

Breadboard power supplies

One of the easiest ways of getting a decent power supply for projects is using a breadboard power supply. This kind of supply typically fits in the power rails of a pre-defined breadboard type, making it very easy to use.

Those supplies typically receive power from an external source and convert the voltage to values commonly used in electronics, such as 5 V or 3.3 V.

A very cheap and reliable option is shown in figure 1. This power supply, called mb102 (there are other similar supplies that use the same name), can be bought at eBay for less than 1 euro.

Breadboard power supply.
Figure 1 – Breadboard power supply.

This power supply has two pairs of pins whose voltage can be independently selected between 5 V and 3.3 V, by jumpers. Those pins are the ones connected to the power rails of the breadboard, in figure 1. It also has 4 pairs of fixed voltage pins, 2 of them at 5 V and the others at 3.3 V. The maximum output current is 700 mA [1].

This device can be supplied by its female USB socket or its DC barrel connector. If using the barrel connector, the input voltage should between 6.5 V and 12 V [1].

Here is a very detailed analysis of this module.

AC-DC adapters adapted as power supplies

Please keep in mind that this method involves dealing with AC currents, which can be dangerous. If you don’t feel comfortable with that, please don’t use this method. I take no responsibility for any personal or material damage that can be caused by following it. This was tested with the Portuguese power grid for small DC output voltages (less than 9 V). Please, be careful.

Another cheap way of getting a reliable DC power source is by cutting the tip of a AC-DC transformer and splitting both wires. One of them will correspond to the GND and the other the VCC. Although they are typically differentiated by color, always double check using a voltmeter.

Other option that avoids cutting the wires is getting an adapter with a DC power connector and connect it to a female barrel connector, as shown in figure 2. That way, you can access GND and VCC through the connector’s legs.

AC/DC adapter connected to a female barrel connector.
Figure 2 – AC/DC adapter connected to a female barrel connector.

Some safety tips:

  • Cut the wires with the adapter disconnected from the power grid;
  • Connect the wires to the circuit with the adapter disconnect from the power grid;
  • Carefully isolate the wires with tape after they are connected to the circuit and before connecting the adapter to the power grid;
  • Don’t let the two wires touch each other, to avoid short circuits.

Batteries

One of the most obvious solutions for power supplies is using batteries. Batteries are portable and are the obvious choice for projects that need to operate autonomously.

Besides that, in order to get different voltages, it’s possible to put two or more batteries in series. Nevertheless, creating a stable structure to hold batteries in series may not be easy for everyone. To solve this problem, there are multiple battery holders available on the market, as shown in figure 3. Those can be bought at a very low price at eBay, where you can just do a quick search by “battery holder”.

Battery holder.
Figure 3 – Battery holder.

Although batteries are cheap and easy to obtain, using them in the development process may not the best option, since they will eventually discharge with usage.

Suggested Readings

References

[1] http://www.sivava.com/k07-ywrobot-3-3v-5v-power-adapter-for-breadboards-arduino-board.html

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