Introduction: Simple Compact 5v Voltage Regulator With Low Battery Alarm
In this instructable I will show you how to make a very nice 5v voltage regulator which will also warns you, in a very annoying manner, that your battery is running out. This is based on MicroScream circuit, published back in 2004. I came up with the compact layout and the addition of an actual regulator. See the attached video for the final product.
A bit of history: I used to fly DLG's, which stands for Discuss Launched Gliders. This is a very addictive branch of the RC modelling sport. The idea is to throw the glider by the wingtip as high as you can and then stay up for a designated period of time. You can find bunch of movies on YouTube, highly recommended. These glider are pure hi tech - composite structure, advanced airfoils and costly equipment inside. They are made as light as possible. There was a time that we used 2s LiPo batteries regulated down to 5v as an on board power. This is when I came with this regulator. The device itself is a voltage regulator, with smoothing capacitors on input and output. It is paired with small, two transistors + 3 resistors + buzzer, circuit that warns you if the main battery, 2s LiPo in this case, drains below a certain value.
The unit weights only 5gr ready to use. It is a linear regulator - no RF interference, and can handle up to 1A of current and it is an analog circuit. I made and sold around 200 of these, and I would like to think that somewhere there are several of these still in the air :).
I don't make them anymore, but I though that someone could benefit from the simplicity and the compact size which can be used not just for airborne purposes.
I tried to make this guide as clear as possible, hope you like it.
Check what G is doing today :)
Step 1: Schematics, Preliminarities and Parts List
Please note, I got the capacitors mixed up in the schematics: 22uF should be on the output, 0.1uF on the input. Just like in the description.
Thank you Josehf Murchison!
This circuit regulates 2s LiPo (7.2v-8.4v) down to 5v constant voltage. The alarm sounds once the input voltage drops below 7.2v=3.6v per cell. Note that it monitors input voltage only, so in any case you will always get regulated 5v as output.
First thing first, decide on the alarm voltage. This is an analog device, so everything should be set in front. The way to adjust the alarm voltage is to change R1. In this case: R1+R2=4.7+2.49=7.19 - slightly below the desired 7.2v. Go ahead and change R1 if you want something else, keep R2 as it is. Keep it slightly below the desired value to allow for hysteresis.
Second, part list:
1. Voltage regulator, AMS1117 5.0V. There is also 3.3V version of this IC, so choose the right one.
Data sheet: http://www.advanced-monolithic.com/pdf/ds1117.pdf
Where to buy: http://www.ebay.com/itm/10pcs-x-AMS1117-5-0-5-0V-...
2. 2N7000 mosfet
Where to buy: http://www.banggood.com/10-Pcs-2N7000-NChannel-Tr...
3. TL431 shunt regulator
Data sheet: http://www.ti.com/lit/ds/symlink/tl431.pdf
Where to buy: http://www.ebay.com/itm/ST-MICRO-TL431CZ-TO-92-3-P...
4. Buzzer, any 5v active buzzer will work
Try this one: http://www.banggood.com/10Pcs-5V-Electromagnetic-A...
5. Proto board: http://www.banggood.com/Wholesale-DIY-Prototype-P...
Or any leftovers that you have at home.
Resistors and capacitors you can choose out of many affordable sets.
Step 2: Prep Your Board, Solder Regulating Circuit
First thing is to cut your board parallel to the short side, as to have strip with 5 holes width.
This strip is enough to make two regulators, because this is so simple and convenient, I'm showing the full procedure for two units. The first picture shows the components for two circuits.
Second, AMS1117 is the only SMD component in this circuit, it needs prep with small drops of tin on the board, note the 3x2 tinned points.
Third, remove one copper dot from each side (one for each regulator).
Next, put the regulator on top of the dots and head with soldering iron, it will melt the underlying tin and will connect the regulator.
Next, insert the two capacitors and the R1 through holes and bend towards the AMS1117. 0.1uf goes on the input, 22uf goes on the output terminals. Pay attention here, electrolytic capacitors (22uf in our case) have polarity.
Solder together with the AMS terminals, don't be shy on the tin here.
The regulating circuit is ready.
Step 3: Solder on the Resistors
Add the remaining resistors. Note the shift in holes.
The R1 and R3 are both connected to the + terminal (that is why we have the shift with R2)
Step 4: Add the Semiconductors
First, bend the legs of the transistors like shown in the picture.
Insert the legs through the holes, note that they share two of the three legs.
Connect the legs like shown in the pictures, follow the diagram for clarity.
Step 5: Cut the Board, Connect the Buzzers, Connect the +
Now it is time to cut the board in half, remember that we are making two units.
Bend the buzzer's legs and solder them as shown.
Note that the drain leg from 2N7000 goes directly to the negative of the buzzer.
Finally, connect a short wire from the battery + to buzzer + (green wire in picture)
The unit is ready.
The video shows it's functionality. Note that the output voltage is not affected by the signal and it is always stable. In order to stop the alarm you need to recharge the batteries
Step 6: Add Leads, Shrink, Use
Now, add suitable leads with your choice of connectors. Note that the negative leg is common.
In my case: female JST on the input and JR servo on the output.
Add a stress releaf near the solder points of the leads - dob of silicone or hot glue.
Shrink the whole unit, allow the hole of the buzzer exposed in order to buzz.
You are all set!