Wednesday, June 24, 2009

RF Transceiver Module...

As mentioned by 9W2DTR, the RF transceiver modules we ordered have arrived. It's a 433MHz module capable of max speed of around 115 kbps, tx power of 7dBm and SPI interface.

Since I'll be doing my development on a prototyping board, I needed a way to mount the module. The module's headers are 0.5mm, 2.0mm pitch whereas a standard prototyping boards are 0.1" pitch. A quick clicking on Eagle, and a few minutes later, the adaptor was born. Photo above shows the RF module mounted onto the prototyping adapter and it is sitting on top of the Futurlec PIC18F4550 development board. The 0.1" headers are reverse mounted on the PCB, i.e., the header protrude on the solder side instead of the component side. The loose module and adapter PCB are infront of the mounted module.

Photo below shows how the module looks once mounted to the prototyping board. There are still two (2) holes on either side of the headers to allow for jumper wires.

Tuesday, June 23, 2009

High voltage and high current equal to...

some fun...

After my capacitor charger worked as intended, I decided to have some fun with some solder lead and aluminum foil... here's a video of what happened to an ordinary aluminum foil when subjected to the charged capacitor... the 5mm strip instantaneously melted with beautiful spark... too bad it was too fast for my normal camcorder...

High voltage and high current are very dangerous... goes without saying... extreme caution is mandatory...

Wednesday, June 17, 2009

This is weird, but interesting!

fi yuo cna raed tihs, yuo hvae a sgtrane mnid too

Cna yuo raed tihs? Olny 55 plepoe out of 100 can.

i cdnuolt blveiee taht I cluod aulaclty uesdnatnrd waht I was rdanieg. The phaonmneal pweor of the hmuan mnid, aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it dseno't mtaetr in waht oerdr the ltteres in a wrod are, the olny iproamtnt tihng is taht the frsit and lsat ltteer be in the rghit pclae. The rset can be a taotl mses and you can sitll raed it whotuit a pboerlm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Azanmig huh? yaeh and I awlyas tghuhot slpeling was ipmorantt!

Eagle Training Session - Confirmed Date

Further to the earlier blog on training/familiarization on Cadsoft Eagle, the followings are the update:

Venue: Jalan Klang Lama, Kuala Lumpur
Date: 4th July 2009 - 9.30am to 4.30pm
Participants: 9W2DTR, 9W2BON (+4 SWLs)
Notes: Participants should bring own notebook for hands-on session. You may wish to download and review this tutorial prior to session.

Any others, please let me know early so that we can make proper arrangement.

Tuesday, June 16, 2009

MilliOhm DVM Adapter

My recent works with SMPS entails winding of coils and, sometimes, current sense resistor which normally is very low in value. Decided to make the above adapter to measure low resistance which cannot be done using standard DVM. Yet to make it but will update on the usability later. Would be helpful also in tracing for PCB or winding shorts, etc...

2009.06.18 Update: The adapter worked as expected. The only issue is that the current limit resistors need to be 'adjusted' based on the LM317 used. LM317 reference voltage is guaranteed to be between 1.2V to 1.3V. If the resistors are calculated based on 1.25V, maximum possible error is around 4%. It's best to tune the resistor using a digital ammeter. Also note that circuit also measure probes resistance. As such, you need to deduct the voltage drop when the probes are shorted in order to get the actual resistance... If you set the current to 10mA then resistance is 1 milliOhm per 1 milliVolt.

Maybe I program a PIC for that and LED displays later... :-)

Monday, June 15, 2009

SMPS Journey continues...

Last week I was working on high voltage, high power SMPS using the push-pull topology. It worked well as I could charge a 2mF capacitor to 375V in about 5s. Later I had the urge to try out another design based on flyback topology. It manages to achieved the same thing but with simpler setup. The main difference I noticed is that the transformer is now warm whereas in the push-pull topology, the transformer show no temperature rise at all...

Now.... what am I gonna use them for... hmmm....

A baby coil winder was born...

Although the coil winder only had a few weekends at may house, it manages to give birth to a new baby winder as shown below... :-)

Made from an old RC servo motor, the baby winder has smaller shaft (M6) thus I could wind smaller cores. It's a simple setup. The servo electronics was gutted and the power is connected direct to a power supply. The on-off switch is there to control the baby during winding. The bolt was sandwiched between two plastic plates (courtesy of my cnc) and fixed with epoxy. The shiny aluminum foil is for me to count the number of revolution. The setup is running at 60rpm with a 6V supply.

Wednesday, June 10, 2009

Cadsoft Eagle Training/Familiarization Session

I've got a few friends asking me to guide them on how to use the Cadsoft Eagle for schematic capture and PCB production. So, in the spirit of sharing, I'm planning to organize a training/familiarization session on the software.

The session will be held in a friend's office, during a weekend. The room will be air-conditioned with LCD projector available. However, participants need to bring own computer to participate on the hands on exercises.

The basic areas to be covered are: Schematic capture, converting it to PCB, doing some electrical rule check and design rule check, and if time allows, we'll touch on creating own library.

If you are keen, please drop me a line either by the chat box or comments on this blog.

Meanwhile, the software is at Cadsoft and here is the product tour.

Monday, June 8, 2009

Time for some low tech - good use device...

Working on the SMPS means winding my own transformers. Terms like EI-25, ETD-29 started to make some sense to me. Had the opportunity to shop with the devil the other day and I ended up picking up this piece of equipment for about RM100. It's a coil winder... the dial will tell you the number of turns the bobbin make. Works well, simple and effective. The only problem is that the winder shaft is about 10mm diameter whereas all my project cores are small thus would not fit the shaft... hmmm... may be time to see silver hair, 9M2CF, to put his lathe to work... :-)

SMPS Journey Update

After several countless nights without REM sleep and tons of downloads from the net, I finally managed to get my SMPS to work as intended. Final board shown below. Few learning points for me on SMPS.

  • The rectifier diode recovery time is a critical parameter. Consider the switching frequency in diode selection. Slow diode will result in short circuit like behaviour on the secondary.
  • Use of snubber circuit on the mosfet help to reduce the voltage spikes.
  • Filtering and emi protection for sensitive digital circuit.
  • Capacitor explodes with big bang... :-)

Wednesday, June 3, 2009

Quick, Cheap, Reliable UV Exposure Box...

In the spirit of homebrew and DIY, the following UV exposure box is the easiest way to do it... congratulation to 9M2IBR for the journey... click image for link...