Introduction: Weekly Project: Voltoids; Or, How to Make 5V From 1.5V
Yes, you read that project title right; this simple circuit will enable you to generate 5V DC from a single 1.5V DC AA battery. How can you pump 1.5V up to 5V, you ask? It's simple with a little piece of electronic steroids from MAXIM IC.
The MAX1674 IC is a DC-to-DC step-up converter that can take in voltages as low as .7V and crank out a digital circuit enriching 5V. Or, for more finicky projects, the MAX1674 can also output 3.3V. A simple pin-selectable preset determines the output voltage.
There is one small caveat with this project, however. Whether a blessing or a curse, the MAX1674 generates a steady-state output current ranging between 180-420 mA. Therefore, high current projects involving motors won't be able to benefit from this voltage amplifying circuit.
On the other hand, powering lightweight projects involving TTL/LS circuitry or LEDs are ideal applications for Voltoids. In fact, with such a low operating current, the MAX1674 is able to drive a 3.3V LED without the ubiquitous power-limiting resistor. All from a single 1.5V AA battery.
If this project seems beyond your talents, but the benefits of powering a digital circuit from a single 1.5V DC power source sounds enticing, you can opt to purchase a similar circuit from Spark Fun Electronics. Costing less than $10, this clever little device which is designed by Bodhilabs.com is housed discretely on the back of an AA battery holder.
Unfortunately, with this commercial product you are limited to a fixed 5V output and it isn't housed in a cool Altoids tin. Enter Voltoids.
Step 1: How to Build Voltoids
Time: 4 hours
- (1) MAX1674 (Digi-Key #MAX1674EUA+-ND; $5.06 NOTE: this is a uMax device)
- (2) .1mF ceramic capacitor (All Electronics #104D50; $1.00/10)
- (2) 47mF electrolytic capacitor (Electronics Goldmine #G13761; $1.00/20)
- (1) 100K resistor (Electronics Goldmine G497R; $3.50/100)
- (1) 22mH inductor (Digi-Key #308-1533-1-ND; $1.17 NOTE: this is an SMD)
- Or, try this 20mH inductor (Electronic Goldmine #G1325; $1.00/5)
- (1) rotary switch (Electronics Goldmine #G13928; $1.00/4)
- (1) knob (Electronics Goldmine #G14481; $.99)
- (1) Altoids tin (salvaged)
- (1) two-position header pins (BG Micro #ACS1019; $.33/2x17)
- (1) AA battery holder (Electronics Goldmine #G16152; $1.00)
- (1) small perforated prototyping board - optional
- (1) 8-pin uMax adapter prototyping board - optional
Step 2: Board or Freeform?
You can build this circuit on a small piece of perforated prototyping board. If you elect to go this route, you might also want to use an 8-pin uMax adapter for holding the MAXIM chip. Be forewarned, this adapter is not the same as the more common 8-pin IC socket. Although untested, try this MSOP-8 adapter from Digi-Key #33108CA-ND.
If you're more adventurous, you can build this entire circuit freeform. In other words, solder all of the components together without using a board to hold them. Please note that a soldering iron can and will burn off a leg on the MAX1674 with too much heat.
Either way this project is for the advanced electronics builder. Just go slow and don't burn your fingers.
Step 3: Can It
A circular Altoids tin is ideal for holding a retro-looking rotary switch. Drill a 3/8-inch hole in the center of the tin for holding the rotary switch. Make sure there is enough clearance inside the tin for the depth of the switch.
Attach the 2-position header pins at the 12-oclock position around the outside of the tin. Be careful that only the plastic portion of the header pin touches the metal sides of the tin. Glue these header pins into place.
Also, line the inside the tin with an insulated material. An Xbox Jewel Case skin from Gamer Graffix is a perfect fit for this round tin.
Step 4: Get Out(put)
Wire one pole of the rotary switch to pin 8 (OUT; for 3.3V) and another pole to pin 6 (GND; for 5V) for generating the proper output voltage. This switch sets the output voltage that is produced at VOUT.
Wire the battery holder's ground terminal (negative) to the circuit's ground. Connect the battery holder's positive terminal to VIN.
Step 5: Power Up
Double-check all of your wiring and connections. Be especially critical of your solder connections on the header pins. None of your circuit should touch the metal box of the Altoids tin.
Rotate the rotary switch to the desired output and insert one fresh (or, even not so fresh) AA battery into the holder. Using a meter, measure the output from the header pins. It should match the voltage that you selected with the rotary switch.
Step 6: Low-Battery Output Option
There is an optional feature of the MAX1674 that enables an AA battery to supply usable voltages down to .7V. This option is called Low-Battery Output.
In order to obtain this Low-Battery Output option, you will need to connect to resistors to pin 2 (LBI). The values for these resistors are calculated according to a formula supplied in the MAX1674 datasheet.
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