Saturday, January 20, 2018

Simple USB AA/AAA NiMH Charger

This post is about a simple USB powered Nickel Metal Hydride charger with an in depth analysis of how it works.

Parts Needed:


1 18Ω 1W
1 22Ω 1/2W
1 180Ω 1/4W


1 100μF 16V


1 1N4007

Battery Case:

For AA and AAA.


1 Micro USB 




How it works?

As the name suggests it is a very simple design so there will not be a lot of parts used. Here is the run down on what each of the parts are doing.

The circuit is powered by micro USB 5V. The first 100μF capacitor is there to just smooth things out. This capacitor might not be necessary. 

Next comes the Diode, which blocks any back flow from the cells and kind of isolate each cells.

The SPST switch is for selecting the Charging Current. Open for AAA about 80mA, Closed for AA about 175mA. If it is Open both the resistors will be used in series and total charging current will be around 80mA which is okay for AAA cell. When the switch is Closed it shorts the 22Ω resistor so only the 18Ω resistor is in the circuit now which causes the total current to rise to around 175mA which is okay for AA.

If you have a high capacity AAA however that can accept high amount of current you can charge AAA while the switch is in AA position. However if you have a low capacity AA and want to charge it slowly you can use the AAA position for that as well. (I'm talking about switch position). 

The LED is there to indicate the cell is connected and charging. If you disconnect the cell it will stop glowing. 

If you want to charge multiple cells just make the same circuit twice, you might use a common 220μF capacitor in that case.


This one is a dumb charger so won't do any fancy thing. It will keep on charging as long as the cell is in there. So you kind of have to measure the time yourself. For 700mAh cell, in AAA settings you will need around 12-14 hours to charge. For 1300mA AA in AA settings you will need around 8-10 hours. These time measurements are for fully drained cells.


Visit my full blog.

Wednesday, January 10, 2018

Mains Powered Simple Blinking LED

This diagram might not be that useful for what it is but it teaches the use of an interesting component called DIAC.

So what this circuit does is blink an LED and can be hooked up directly to AC main line and it needs only a few components.


1 47kΩ
1 220Ω

1 47µF 63V

1 1N4007

1 DB3


How Does it work?

When power is turned on the 47µF capacitor starts to charge via the 47kΩ resistor and 1N4007  diode. As soon as the voltage hits the break over voltage of the DIAC DB3(Which is 32V, more information in the datasheet linked below) it starts to conduct and the LED lights up.

As the current is passing through the LED now it empties the charge stored in the capacitor faster than what the 47kΩ resistor can provide so soon enough current through the DIAC falls to a point when it will just stop conducting. Thus the LED turns off.

Then the whole process repeats again giving us a blinking LED.


1. Remember that even if the DIAC was triggered with a certain voltage it will keep conducting unless the current through it falls to a certain value. Once triggered, even if the voltage falls below break over voltage it will still conduct.

2. 47kΩ resistor and 47µF capacitor can be altered to control the blinking frequency.

3. This circuit is not mains isolated so to avoid electrical shock do not touch any part of the running circuit.


1. Datasheet for DIAC DB3.
2. More about DIAC.
3. Visit my full blog.

Monday, November 27, 2017

DIY Powerbank 2017-A

In search for an easy to make power bank diagram? Here is one for you.

To keep things easy and simple different modules have been used instead of discrete components which greatly reduces the amount of work to be done however a few capacitors will be needed.

Main features:

1. Use of Lithium Ion cell. 18650 cell with protection will be perfect.
2. TP4056 based Lithium Ion charger.
3. A7530 based DC-DC boost converter. 

Extra components required

2 100uF 16V Capacitor.
SPST switch.

This diagram is easy to understand and make but the main limitation will be the amount of power it can deliver which is not that high.

The modules:

First module that will be used is a TP4056 based single cell lithium ion charger. It charges through a micro USB port which is very convenient. It can charge at up to 1A of current which is moderately fast. This module also has Two indicator LED for showing different status. Link to the datasheet is added to the bottom section of this post where a detailed information on what the indicators mean can be found. The only modification required is to solder one 100uF capacitor on the Input pads, minding the polarity.

4056 Based Lithium Ion charger Module

The second module is an A7530 based DC-DC converter. As you might know the voltage of USB port is 5V where lithium ion delivers around 3.7V-4.2V. So Voltage has to boosted up. This particular module do just that, it has a USB port on the output section that can deliver about 800mA so not that powerful but should get the job done. It comes with a 100uF capacitor on its output so nothing needed there. It also has an Indicator LED on board which will light up during operation.

A7530 based DC-DC Converter

Choosing the lithium ion cell

18650 cell with DW01A and 8205A based lithium ion protection circuit will be ideal for this. If your charging module already have protection you can use unprotected lithium cells as well. Two or more cells could be used in parallel although make sure to use similar cells. The only modification needed here is to add a 100uF capacitor across the cell.


This is how the modules and other parts will be connected. 

Very small amount of soldering has to be done with this project. On the Lithium Ion charging module a 100uF capacitor is soldered across the input pads. From the output of this module two wires run to the Lithium Ion cell. Another 100uF capacitor has to be soldered across the cell. I would recommend using 18650 battery case and soldering the capacitor across it which not only omits the necessity of soldering wires across the cell itself but will also make it easily swappable. From there those two wires run to the DC-DC voltage boost module, a switch can be added between the battery and the boost module to turn it on or off and that's pretty much it. Put everything in an enclosure and you are good to go.


1. Datasheets.
2. My full blog.

Tuesday, November 21, 2017

Single Cell LED circuit with Joule-Thief

If you want to light up a white LED from a single AA/AAA cell with minimum amount of components this circuit will be a perfect fit for you.

Scope of use:

This diagram might not be that useful for serious project but it is awesome as something small and simple to make yet works very well. This circuit can extract energy from AA/AAA cells that might seem empty. Even if other devices won't run on it you can practically get some energy from them, yes a LED won't do much but for very small torch or something it will be awesome.



25Turn of 26Gauge/0.404mm wire on Ferrite Toroid , shown in the diagram.


1 220ohm


1 BC547NPN


1 White LED.


How it works?

To put it simply the top coil in the diagram conducts while the transistor is on and stores energy across it and after small amount of time when the transistor turns off this stored energy finds a way to dissipate and increases the voltage up to a point at which the LED will conduct and which in turn make the LED light up.
If you follow the link below you will be able to learn in more details of the inner workings of this circuit.


1. It is better to use a white LED.
2. If you can't make the coil two 100uH Inductor in close proximity should work as well. 


1. Datasheet for transistor.
2. Visit my full blog.
3. Joule Thief circuit.

Single Cell LED circuit with regular components

If you plan to make a single cell LED driver but not willing to use any integrated circuit and only of the shelf products this diagram is for you.

Parts Needed:


1 PN5143 PNP
1 PN3569 NPN


1 1k
1 2.2k
1 3.3k


1 470pF
1 22uF 16V


1 1N5817 Schottky
1 LED White


1 100uH


How does it work?

This circuit simply boosts up the voltage by switching on and off the NPN transistor PN3569 which in turn stores energy in the 100uH Inductor and released. This is stored to the 22uF capacitor through the Schottky diode which turns the LED on. The switching on and off is done by the PNP transistor PN5143, 470pF capacitor and the resistor with it. You can read DC-DC Boost converter to learn more about the process.


1. Datasheets of the diode and transistors used in this project.
2. Visit my full blog.

Single Cell High Current LED Driver with LTC3490

If you are looking for a circuit to drive high brightness 1W LED with a single dry cell this will a be perfect diagram to use.

Necessary Components:



1. Inductor that can handle 2-2.5A has to be used.
2. To soft turn on the circuit an 1uF capacitor can be used across the 1Mohm resistor.
3. 1W white LED should be used with this circuit.
4. Q current is less than 1mA.


1. Datasheets of the components used in here.
2. Visit my full blog.

Single Cell LED Driver With LT1932

Have you ever tried to turn a LED on with a single AA cell? It wouldn't light right? Because a single cell doesn't have enough voltage to turn a LED on as typical LED forward voltage is about 2V-3V. So if you want a LED to light up with a single cell you will need something more.

In this post I will write about how to do just that but with good components which will be excellent for a bright LED based torch light running on a single cell.



1. Input Capacitor Must be placed as close as possible to the LT1932.
2. Rset value of 1.2Kohm is selected to get about 20mA, for higher current check the datasheet.
3. Low ESR capacitor should be used with the output.
4. Low DCR Inductor should be used.
5. For a long battery torch light single C cell will be perfect.
6. 5mm 20mA White LED with reflector should be a good choice for torch.
7. You can add more LED if you want, check the datasheet


1. Datasheets Integrated circuit, diode and LED used in this post.
2. Visit My full blog.