Rustic Engineering

My Mind working on…

Posts Tagged ‘pcb

Hand Soldering OLED – video

with 5 comments

Hi friends.

Some people ask me about how to do hand soldering on smaller parts, like on my OLED Display Board. It uses a “TAB” (tape automated bonding) or “COF” (chip on flex) style flex tail mated with a “COG” (chip on glass) display. Normally, TAB connector is soldered directly to corresponding pads on your PCB using a hot-bar soldering machine.

I don’t have that hot-bar soldering machine, so my hand’s can make the job. The first time I’ve done this soldering, I was a bit scare about damage the connector. My only tip is “don’t spend much time over the fragile contacts.

For help us, I’ve recorded my last OLED soldering. Maybe can help some people about SMD soldering (as some internet videos help me some years ago).

On YouTube:



Written by forrequi

November 11, 2010 at 16:55

Posted in electronic, LCD, OLED, pcb, projects

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How much current (part 1)?

with 7 comments

Someone send to me a question, about how much current my OLED board consumes at all. Well, after measure with a multimeter the answer is: 660μA (aprox.) with display all ON and contrast at 0xFF (max). But this question make me thinking about how measure that current myself, without a multimeter.

When I’m in graduation (some good years ago) I made a little circuit to measure how much current my power supply project output. The circuit is based on “high-side current-sense” methodology. See my hand-drawn circuit above:


HIgh-side current-sense

High-side current-sense


This circuit is a classic high-side current-sense, where the voltage drop across Rs resistor is isolated by a operational amplifier (op amp) in a differential configuration with unitary gain. The many implementations of technic were based on discrete components or semidiscrete circuitry. In their simplest form, such high-side monitors require a precision op amp and a handful of high precision resistors.

The resistor value should be low (like mΩ scale), to minimize power losses, but don’t be too low, because stability problems. And don’t forget about power dissipation across the resistor.

One common approach for high-side measurements has been the use of the classic differential amplifier, which is employed as a gain amplifier.

So, after reading a lot of theory, I’ve going to search my integrated differential amplifier.

Integrated Differential Amplifier

I should admit: Maxim is always my source of good op-amp IC, so I’m was doing some search and found a good and little evil: MAX4372. Some goods about this guy:

  • Tiny SOT23-5 package;
  • Low cost;
  • 3 gain options (20V/V, 50V/V and 100V/V);
  • +2.7V to 28V range of operation;
  • Consumes only 30μA;
  • 0.18% full-scale accuracy with 100mV Vsense input (This is equivalent to only 0.18mV input offset voltage);


MAX4372 typical use

MAX4372 typical use


The MAX4372, in a tiny SOT23-5 package is a very good device to make a current sense device. You can set the full-scale current reading by choosing the device:

  • MAX4372T: 20V/V Gain;
  • MAX4372F: 50V/V Gain;
  • MAX4372H: 100V/V Gain;

What means 20V/V Gain? If you have 1A current flow through a 100mΩ Rs resistor, you gave only 0.1V drop. But with 20V/V, you multiply this and obtain 2V. Obviously? The design goal with Gain is thinking in terms of full scale design. If your A/D converter uses 3.3V was reference, you can consider this to check what the max current value you can measure with determined gain value.

A test circuit

I’ve designed a test circuit to test my idea. Basically is a MAX4372T with a 100mΩ Rs. I’ve mounted it in universal board, and my idea is connect it to my USB Low Pin Kit:


MAX4372 basic circuit



Test board


To test them, I’ve used a PIC18LF2520 and a great character LCD from Electronic Assembly. See my test circuit working:


First test



Looks great!


The pictures show that the global idea works great. Now I need some work to improve stability and other features.

Next steps…

The next step is create a USB device for read, store and show the current measurements:


USB Power Monitor

USB Power Monitor


Written by forrequi

October 17, 2010 at 03:02

Lithium Polymer Battery USB Charger

with one comment

Finally I’ve finished this project. It’s a USB Charger for Lithium Polymer Battery, that’s very compact and high powerful batteries that I use in most of my projects.

A tiny and elegant charger...

All sides...

In my recent GUI Bot project I’ve used the famous MAX1555, a greatest IC in a tiny SOT23 package. One thing about MAX1555 that I don’t like is the current limitation it has (about 100mA). I know it’s for USB low speed compatibility, but who knows someone that don’t have a high speed USB host surround? Because that I use the greatest MAX1811. It’s a great IC too, but can deliver up to 500mA! See one of my first post to check more details.

That’s the finished work:


If anyone like this circuit, email to

Written by forrequi

March 10, 2010 at 23:40

USB Small Peripheral Board (aka PIC18F14K50 Board) Finished

with 17 comments

Well, my board comes to me yesterday and I’ve soldered all parts. The board is really small, very compact, very robust. I’ve made a little test only to check if are something wrong, but not. Everthing works well. Very good for version 0.

See the photos:

Finished and empty PCB

Breadboard friendly

Programming via PICkit3

Now, I (and you, please contact me if you like it) can test and make nice devices, without boring with crystals, capacitors, reset, USB it self. You can attach it on a breadboard or your own prototype PCB with your circuit.

I’ve created a kind of pin card, for rapid pinnout reference. I got the card idea from Mbed project. It’s very useful, with all pins and ports plus the information about device peripherals.


Reference Card (like

Think the nice things you can do… I want to make a test with USB Mass Storage Device, yes, a Flash Drive. I’ve a little project where this really help me with configuration storage, etc.

For test, I’ll show us some application example, like a USB RFID reader.

RFID Reader

If you like this board and want to get one, email me to talk about. It’s a zero version, so some errors could exist.


Eagle files here.

Written by forrequi

March 5, 2010 at 00:17

USB Small Peripheral Board (news!)

with one comment

I haven’t finished my last board yet and other are designed. That’s time with USB connector made with the own PCB. Thank’s to Sparkfun for the Eagle library, that have this option of USB port. Now more then one version is comming!

I hope us enjoy this board when it’s arrive. See it:

Written by forrequi

January 3, 2010 at 22:38

Posted in electronic, pcb, projects, USB

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