Thursday, March 27, 2008

Reference on Various Sound Pickup Circuits

Since my venture into the 'remote' mic for the mobile rig, I've been searching for more ways to improve the sound quality. Came across the following website which prove useful as reference.


Wednesday, March 26, 2008

APRS Information / Kits

The amateur radio in Kuala Lumpur recently held a knowledge sharing session regarding APRS (?)... Unfortunately I was unable to attend due to personal commitment... It is a subject of interest to me so I search the net further for more information... then, being an electronics maniac, I started thinking what to make or buy :-)

Came across the following website providing various products with full schematic, firmware, pcb layout and the rest... a commendable effort by the owner of the site, Dinesh Gajjar. Clicking the image will take you to his APRS section... go check it out...



Monday, March 24, 2008

Update to microphone circuit...

After less than ideal performance using the unit below (hissing on high gain, whining from engine noise, hollow sound, etc), I did some more digging on the net to look for possible fix... I find this article/document to be very informative and deserve a mention here on my blog for others to checkout...

I'll be changing my opamp tonight with one that has very low 'input bias current'... I have a few LMC6081 on hand and I'll use those... the opamp I use now is CLC449 (obsolete) with about 50uA input bias current... the LMC 6081 is spec'd for 100pA! Orders of magnitude lower than the CLC449...

I'll add the output and grounding resistors as suggested by 9W2DTR... I'll set the output resistor to 100R and the ground resistor to 100k... I'll add some ferrite beads on the power lines as well to tackle the engine noice...

I will update on the performance later... stay tuned... :-)

Update: March 25, 2008
The fixes above worked... audio is cleaner, clearer, louder with no whining...

Friday, March 21, 2008

Remote MIC and PTT switch for Mobile Rig

I have always wondered why there is no 'hands-free' kit for ham mobile rig... For the handy/portable, you would have the whole range from normal PTT to throat mic to bluetooth unit...

Typical for any mobile rig, you would need to bring the mic to your mouth and press the PTT to talk... I'm not sure what the law actually state, but I assume it's illegal to do this, since talking on the mobile phone without a hands-free kit is illegal here...

So I came up with 'look-like-hands-free' for our mobile rig... It's basically a simple opamp-based electret mic pre-amplifier with very minimal gain and the switch for PTT... The red button is the PTT button and a spare connection is provided near the RJ45 jack for additional trigger... The mic is a normal tie-clip electret mic... The wiring are done for my Kenwood TM-V708 mobile rig but it can be fitted to almost any rig... just need to identify the correct wiring to use...


So, with this unit, I would clip the microphone to my shirt or collar and the box will be somewhere near my center console... pressing the button will not be obvious anymore because it's no longer done within normal field of view... Here's the photo of my 'looks-like-hands-free' mic and PTT for the mobile rig.... :-)

Get the Schematic & PCB Files

Wednesday, March 19, 2008

New Blog Created for PIC Lessons

Update: CNAME has been updated. The blog can be accessed using pic.9w2bsr.com

As some of you already know from here, few of the regular gangs will be starting our PIC exploration soon... To facilitate that and to avoid clutter to this blog, I've setup another blog for that purpose... for the moment the site is very bare but expect it to be very active very soon... the link is here... very long until my CNAME is updated...

Monday, March 17, 2008

Deciphering Battery Voltage

9W2RYZ gave me the following chart which prove useful to those trying to decipher the car battery voltage... BTW, I have coded a new firmware for the battery monitor to do the followings:

The display will alternate between various readings:
-C- realtime voltage; -L- lowest voltage; -H- highest voltage; -T- trend.

For trend, ^t_ indicates declining voltage; -t- indicates constant voltage (<0.2v); onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="http://4.bp.blogspot.com/_tMtO23Q5vm4/R93ZJINI8qI/AAAAAAAAATs/DG0vpe0CDv4/s1600-h/Battery-Chart.gif">

Thursday, March 13, 2008

Alternative Bluetooth for Amateur Radio

Upon future exploration into the Bluetooth foray, I came across this module on Amazon that might fit the bill for most Amateur Radio bluetooth conversion. It basically connects to your rig speaker and microphone jacks. After the normal pairing, QSO can then be done on a bluetooth headset. The only drawback is that it doesn't have option for triggering your PTT, thus limiting your QSO to VoX basis only...


Teaser for 9W2ALT and 9W2LYZ...

Here is the startup display of your voltmeters...
They just underwent 7 hours of burn-in test last night...
No problem...
On the topic of battery monitoring, note below is extracted from Wikipedia...

These are general voltage ranges for six-cell lead-acid batteries:

  • Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell)
  • Open-circuit at full discharge: 11.8 V to 12.0 V
  • Loaded at full discharge: 10.5 V.
  • Continuous-preservation (float) charging: 13.8 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.4 V for flooded
  1. All voltages are at 20 °C, and must be adjusted -0.022V/°C for temperature changes.
  2. Float voltage recommendations vary, according to the manufacturer's recommendation.
  3. Precise (±0.05 V) float voltage is critical to longevity; too low (sulfation) is almost as bad as too high (corrosion and electrolyte loss)
  • Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation)
  • Equalization charging (for flooded lead acids): 15 V for no more than 2 hours. Battery temperature must be monitored.
  • Gassing threshold: 14.4 V
  • After full charge the terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V.
For more information, click here

Wednesday, March 12, 2008

Sorento Fuel Consumption Chart

To my Sorento gang, here my fuel consumption chart for the past 65,000km... Long term average is 9.00km/l... Almost 100% using Shell Diesel... Refueling primarily in Taman Desa, KL with occasional outstation refueling... click image for larger picture...

Monday, March 10, 2008

Laser-based referencing...

I received the laser modules I ordered from DealExtreme last week... Of the lot, I ordered a few that output cross-beam... These were meant to be used on my Sherline as a referencing tools (sorry 9W2GU, another cnc enhancement).

Here's how it was modified... Take the module apart but don't remove the laser from the center piece... Enlarge the original hole at the back (where the wires were) to fit suitable shaft... I used 6mm countersunk screw so I enlarge the hole to match... fix the shaft to the back case... then drill new hole on the side (diameter 3mm or larger) for new exit point for the wires... carefully reassemble... chuck it in your spindle, lower it to your preferred height and focus the lens for a finest line...

For alignment, drill a small hole on any workpiece... then without changing x-y, chuck the laser module in... adjust/tilt the focusing lense so that the lines cross exactly on the drilled hole... Loctite the lense, let it set and you're done...

The modified module...

The result on the Sherline... I was able to focus the lines to about 0.25mm in width... pretty good for a USD4 module and 15 minutes hack...

Thursday, March 6, 2008

Simple 2 input NAND circuit

Someone asked me to troubleshoot a problem... not sure what the circuit looked like... this is one possible way to do it... question or discussion via the chatbox or comments, please...

More explanation can be found here...
BTW, I'm no electronic expert... just a tinkerer who has burnt my fair share of chips, transistors, fuses, and so on... :-)

Battery Monitor Unit - Updated

The update on the automotive battery monitor project... Design, prototype and coding done... The unit will flash the display if voltage drops below 11.0V or exceeds 15.0V... like everything else, the limits are programmable (not by end-user, advise when ordering)...

I'll offer two options... cased and tested PCB... the casing I'll use will be basic... for nicer casing or direct mounting to dashboard, get the uncased version...
Next photo shows the indicator mounted in the intended casing... ignore the side hole... it was there from a previous project... I didn't have the opportunity to buy new casing... For those who do not like to see the white characters, we can apply the red filter in-front so the character only visible when lit up... BTW, the paper clip used to tilt the unit is not included... :-)

Monday, March 3, 2008

Amateur Radio Rig to Mobile Phone Bluetooth Earpiece

I had the idea of linking a normal mobile phone bluetooth earpiece to an amateur radio tranceiver using a homebrew bluetooth 'enabling' box. After toying with idea for a while, it daunt upon me that the final price for such box would be about USD150... may not be off interest to many of my gangs...

Well, for those interested on the unit still, there's good news and bad news... the good news is that the box is ready for sale... by someone else... checkout the TalkSafe product range from this site. The bad news is that the price is not attractive enough for me... will explore other options still...