Friday, November 29, 2013

How to set up a EE lab / Hobby workbench at home

5 simple tips for a removable hobby bench.

Space inside the house is not something many of us have these days.

The following are some recommendations on how to transform a space in your apartment into an electronics hobby bench.

1) Tip#1: Extendable dining table.
Not a must, but a very nice to have.

2) Tip#2: Good lighting. 
Change the bulbs on your ceiling so it is at the level you need. Be creative and build your own ceiling lamp to balance beauty with functionality. Or buy something that will illuminate your bench accordingly.
You can also add a desk lamp such as this:

3) Tip#3: Yoga mat, and even better: ESD mat.
This is a must. This not for relaxing (your hobby is actually for that).
It's to put over the table. It is non-conductive and it will not develop static electricity either.

It will accomplish the following:

- It clearly defines your working area. Easy to trim with scissors to the dimensions you like according to your own preference and arm length.
- It prevents small parts and screws from bouncing off the table and thus it will save you hours and hours of looking for them. Small screws always end up in the most unimaginable places when they bounce off the table, and you know it. Do the test and see how well this mat will absorb shock from falling parts.
- Provides comfort and warm and soft feeling for your arms.
- It will protect your dining table from scratches.

- It provides a cushioned area for your projects or to-be-repaired objects without scratching or damaging them (imagine disassembling an iphone on top of this versus the wooden table).
- It allows you to rapidly clean up your working area. Just lift it and empty thousands of cable insulator and bits of solder and sweat and blood directly on your trashcan! All in one single motion.
- It will eventually get stains and will melt when accidentally aiming your rework station or hot glue gun or soldering iron. You can always get a brand new one for a few dollars.
- And it's easy to fold or roll when not in use.

4) Tip#4: Get the basics

Depending on the nature of your hobby, your mileage may vary.

 To me the essentials are:

- A soldering station.
         Also solder wick and a good solder pump.
- A third hand and a Panavise.
- Tools. To your preference. Check for Collin's Lab: Electronics Tools
- Build an ATX power supply (for sense of accomplishment and endless use of 12V, 5V and 3.3V power with short protection and temp auto-shutdown). I like Jumper One ATX power supply. Add variable voltage capability with an LM317 Another one from JumperOne.
- A decent multi-meter. No need to go Fluke. Just nothing below $40 and you'll do fine.
- An oscilloscope. (You won't need it for general hobby use but eventually it will become helpful).
- A small table-top trashcan to toss your small bits of unwanted material.
- A digital microscope on the cheap: It's not easy to read chip labels or inspect soldering with your bare eyes. Get a manual focusing webcam and use it as a microscope (8 bucks).
- A rework station. For melting hot glue, shrinking heat-shrink tubing and yeah, to rework stuff.
- Isopropyl Alcohol, Q-tips for cleaning. I use it all the time.
- Small parts plastic organizer for putting in screws of the things you disassemble.
- A separate box for unfinished projects and less-used parts, which reminds me of..... step 5:

5) Tip #5: 5S your place.

Seriously. This is by far the most important piece of my advice. If you are not a 5S kind of person, become one. This is vital to be able to enable and disable your lab at will.

Don't know what I'm talking about? 5S describes how to organize a work space for efficiency and effectiveness by identifying and storing the items used, maintaining the area and items, and sustaining the new order. Read More

This means: Get toolboxes, drawers, stackable parts bins. Label and outline tool placement. A place for everything and everything in its place. Measure of success is to be able to put your lab together in 15 minutes and put it all out in 45 minutes (it takes longer to store it out because you end up with new stuff to find a place for, cleaning duties and you are generally more tired and slow). Improve until you succeed.

B) Bonus: Take it one step further

You are most likely skilled at DIY already, so grab your tools and build your own shelf, custom made to your own needs just like this wooden shelf for the Power Supply, scope and multi-meter:

Monday, October 7, 2013

Smartphone Signal Generator

How to build a small amplifier for your smartphone signal generator

You can find plenty of signal generating software for both Android and iOS devices.
Here's an example of Audio Tool for iPhone and iPod Touch. They obviously range between 20Hz and 20KHz (human audible range) because audio output of these devices is meant for music:

However, the voltage ranges of operation are pretty low.

Building a small amplifier for your phone:

I started out from Amanda Ghassaei's Arduino Waveform Generator.

Since the function generation piece of her circuit will be entirely replaced by the iPhone, I just built the OpAmp piece as follows:

I used alternative parts to replace some of these suggested components, starting by the OpAmp, then following for the 22K instead of 20K resistor, and 25v capacitors instead of 50v. Feel free to use slightly different components. 


Building process: Note how the SMD chip levitates on top of the board. I chose pins for easy grabbing with alligator clips or scope hooks.

And the finished product:

The two contacts at the top are the power in connectors.
The other two at the bottom are the signal Out terminals for your part or your scope or both.
The signal is fed from the Smartphone via the cable at the side. The triple white wire goes to the potentiometer. 


Thursday, August 1, 2013

Battery powered Atari 8-bit


You may have read my post about how to power an Atari diskette drive with a switching power supply.

You may have noticed that I'm not a big fan of heavy, large Atari power bricks.

And don't get me wrong: they are beautiful designs, reliable, powerful, and Atari branded. However, in modern days where an 8-bit is not your primary computer for getting things done, these bricks make it unappealing to get your vintage gear running every once in a while.

The objective of this easy project is to be able to pull your Atari from an UV-free storage and hook it up to your TV allowing quick play using a SIO2SD interface.

So here it goes: A battery powered 8-bit (With the battery inside the case).

Materials needed:

- An Atari 8-bit computer willing to be modded in the guts. (I've used a spare 65XE since I would never mod an 800XL in any way).
- A battery. Lithium Polymer 11.1v / 3-cell, 1800mAh and above.
- A switching voltage regulator aka DC to DC converter: I used a 5v OKI-78SR series from Murata Power Solutions.
- Decent soldering skills, a soldering station and powerful de-soldering pump.

Do some research first, ask yourself some questions:

Q: Can an Atari be battery powered for a decent amount of time?
A: Atari power bricks supply a maximum of 1.5A, if you measure the actual consumption at 5V it goes around 450mA which is not hard for a LiPo 12V battery to handle.

Q: How long will the battery last?
Once using a regulator, it draws only 250mA from your battery, giving you a theoretical life of 4 hours of continuous play on a 2100mAh battery. I'm fine with 1 or 2 hours and this easily doubles that!

Q: Will a battery fit inside the case?
A: There's only one way to figure it out: Crack your machine open and see what fits in. The 65XE has quite a roomy case for this mod. I'd say it actually fits two batteries.

Q: Should I use a linear regulator or switching regulator?
A: The problem with linear regulators such as the LM7805 is that you waste too much energy in heat and in this case it will get fairly warm, which will force you to add a heat dissipation on a tight space. The switching regulator is far more efficient and not noisy enough to disturb the functionality on your Atari. Audio comes out fairly clean with these.

The design:

This design considers interrupting the 12V line. If you do it at the 5v stage after the regulator, you can easily solder the circuit directly to the 5v connector on the motherboard. However, this won't work best because the regulator will continuously draw current from your battery until depletion. Not good.

On the other hand, interrupting the battery feed directly like the diagram shows, will force you to add a secondary switch or de-solder the original switch.

Caveats on the design:

  • This design requires you to understand LiPo batteries because these are delicate and potentially dangerous. 
  • You will need good soldering skills and take the necessary precautions while connecting everything together and isolating the connections properly.
  • You will need a special charger to take care of the life of the battery as well as to prevent overcharge.

Regulator placement

The three legs of the power switch were de-soldered from the main board and isolated. This power switch now handles 12v instead of 5v.

Final battery placement
Project finished, ready for the final cover.


Charging gets accomplished using a special LiPoly charger directly to the balancer connector of the battery. That connector reaches the exterior of the case via the expansion port. If you look closely the last picture you will see a white connector sticking out.

After finished, I left it on by accident and noticed almost 3 hours later. 
The battery was at 11.7v, plenty of life left. But this definitely reminds me of the....

To Do

Add a low battery automatic shutdown to prevent damage to the battery.

Thanks for watching, stay tuned.