Stripboard Magic is a Windows application for designing PCB layouts on stripboard (aka prototyping board). It was released by a British company called Ambyr which ceased trading a long time ago. The interface is a quite primitive and a little strange but the program is functional even on Windows XP. It also works great in Linux using Wine. Continue reading
Subaru Legacy McIntosh subwoofer hack
Here’s a quickie on adjusting the gain of the OEM-supplied McIntosh subwoofer in many BE and BH series (MY 1998-2003) Subaru Legacy’s. The subwoofer gain and crossover frequency is non-adjustable, at least until now. : ) If you have such a car and want to get a little more punch from the sub, read on!
The amplifier is bolted to the floor under the drivers seat and has two connectors on the end closest to the door. Disconnect and unbolt the amplifier and take it apart. Make a careful note of where each screw goes as they are not interchangeable; you can permanently damage the amp by shorting things out of you replace the screws incorrectly.
Find R519 on the underside of the PCB near the power and speaker connector. In station wagons this is rated at 10k and in sedans 4.7k, labeled as either 103 or 472 respectively. This resistor sets the negative feedback in the final stage of the subwoofer crossover.
Replace this resistor with a higher value to increase the gain. Don’t leave it out of the circuit or it may overdrive the sub and do damage. If you short it you will mute the sub entirely.
After some experimenting I feel 33k delivers quite a nice bit of punch in a station wagon, which should boost the sub by about 5.2dB. Feel free to choose any value you want between 10-100k. Be careful using high values as it becomes quite easy to inadvertently overdrive the sub.
You might want to use a potentiometer instead so you can adjust the sub gain as you please. If you do this, I suggest a 50k linear (type B) pot in series with a 10k resistor. Make sure you use shielded cable and keep the cable very short to help prevent any instability in the amp. Connect the cable shield to a suitable ground point in the amp and (ideally) a 100nF or similar capacitor between the cable shield and the pot casing to prevent possible ground loops.
Enjoy!
Multiplexing 7 segment LED displays with Arduino
Here’s an example on multiplexing three seven-segment LED displays from an Arduino using a single 4511 IC and a handful of transistors. This builds on my last post about interfacing to a single display
Making PCBs
Here’s a brilliantly simple article on making PCBs at home.
I’ve tried a few times with the toner transfer method but using magazine paper looks to be very effective.
Sharp Carousel microwave LCD repair
The LCD on my Sharp microwave oven recently failed, beginning with a few segments but quickly getting worse. I’ve seen quite a few similar models with the same problem and a quick Google search proves this. Sharp even offered a recall at one stage.
If your microwave oven suffers a similar fate and you could give this a try. Note that it is not actually an LED display as some seem to think; Sharp have simply done a pretty convincing job of making the LCD look like one. Continue reading
Japanese import FM tuner conversion
This post describes how to modify a McIntosh PF-2142I (often but incorrectly referred to as PF-21421) JDM car radio to natively tune from 87.5-108MHz as used in most countries around the world. This model of radio is fitted as standard equipment in many JDM Subaru Legacy and Outback cars manufactured between 1998 and 2003. Continue reading
Brother HL-2150N in Ubuntu Karmic
Normally I try to stick with HP printers when using them in Linux as they seem to have the best support thanks to HP’s efforts with HPLIP.
I recently went against my own advice and purchased a Brother HL-2150N monochrome network laser printer. Brother have at least tried to provide drivers for Linux and even supply Deb packages. Unfortunately installation is a mess involving ugly binary wrappers and packages that don’t appear to conform to Debian policies very well.
Whilst there is no official support for this printer model in Ubuntu 9.10, it can be set up to work via Ethernet fairly easily. Continue reading
Flash drive fakes
Against my recommendation a relative recently bought a 32GB USB flash drive off Trade Me. It cost something like $85 when such drives are currently about $130 at wholesale rates. Continue reading
Simple Arduino 7 segment display example
It appears that there are many different ways to interface a seven segment LED display to the Arduino; the humble 4511, 74HC595 shift register and a multitude of fancy (and expensive) serial ICs such as the MAX7219.
I decided to use a 4511 driver IC for this purpose as it was the only suitable chip I had lying around. It saves a few pins over driving the display directly from the Arduino and also works from a wider voltage range so can be used for driving large display modules.
McIntosh EF-1080I silent output fix
I recently acquired a McIntosh EF-1080I car amplifier that was almost completely dead. There was a small amount of sound coming from the speakers but it was quite distorted.
With the amp opened up I measured the +/- 26V and +/-15V rails and all were fine. I then concentrated on the muting circuit seeing the problem affected all channels. If you need to open one of these amps, take a note of where each screw goes as replacing them incorrectly can permanently damage the amplifier.
All of the channels in this amplifier model are based around the TDA7295 by ST Microelectronics. This chip features standby mode and muting on pins 9 and 10 respectively. Both must be held high (5v) for the chip to operate.
The power supply section of the amp has a de-thump circuit that pulls these pins low for a small delay at power on and immediately after power off to prevent noises in the speakers. Unfortunately the mute pin was staying tied to ground.
I traced the problem to SMD transistor Q607 that normally switches all of the mute pins. It actually disintegrated while I desoldered it, and replacing it restored the amp to life.
The transistor bears the marking IY and is in fact a 2SA1162 general purpose PNP transistor. I replaced it with an identical part, however a friend suggested replacing it with one of a higher current rating such as a FMMT591. The FMMT591 works fine as a direct substitute and has a maximum rating of 500mA so should be a lot more reliable.
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