Vintage headphones mod – The ultimate hipstery conclusion

I started this blog by modding some “vintage” headphones, replacing the original bad speakers by a pair of Sennheisers. It was almost two years ago.

Last month finally happened what usually happens to audio jack cables: “qsdfg#efdfg#jnd#qdfg#skdglcvnqse” instead of my usual music (which is almost the same, but without the “#”s ).

I decided to totally pimp the new cable by using one of those “fabric 220V cables”. I had the idea for a while, but I didn’t realise the fabric covering isn’t actually glued to the cable and you can use it on an other cable.

I got one on eBay, 1.99€/metre, plus a 5-metre long jack/jack cable of reasonable quality:

01-Fabric-audio-cableI cut the audio cable in half so I can still use the other half for something else (or as a spare).

The fabric covering is very easy to strip (it slides off) but more difficult to put back. It was a good idea to put tape on the cut end of the audio cable, so it could slide easier.

Then, I just glued the fabric to the jack plug and secured it with a cable tie when it was drying:

02-Fabric-audio-cable

Soldering the cable back in the headphones:

04-Fabric-audio-cable(you can see how easily the fabric strips off and also the tape at the end of the audio cable to help with the sliding-in)

After, I added some turns of thin electrical tape, to avoid the fabric fibres to strip out:

03-Fabric-audio-cable

Et voilà:

Headphones1(After testing the new cable, I realised it was the audio socket of my iPhone that had a problem, not the headphones’ jack.. )

Simple and cheap temperature logger: v2.1 [UPDATE: EEPROM in BOM corrected (SST25WF080) ]

Hi everyone!

It’s been too long since the last update. But it’s there! The last version of the temperature logger, the hardware and the source code.

USB-Temperature-Logger---Component-side

USB-Temperature-Logger---Battery-side

The changes since the last version:

Hardware

  • New footprint for the PIC18F26J50, easier to solder.
  • Only 0603 or bigger resistors/capacitors.
  • The serial EEPROM is now a SST25WF080, still 8Mb, but easier to source.
  • Some components price-optimized (USB connector, switch, 3.3V reg).

Software

  • Each logger can get a number, shown in the mass storage device drive name: simply add an asterisk (*) followed by the number you want to assign to the logger (between 0 and 65535) in the config.txt file (after the logging period), save the file and format the logger.
  • Bug fixes in the FAT12 functions, but the logging space is still limited to the half of the EEPROM.
  • Other bug fixes (month and year change, added robustness). The memory and the EEPROM are now scanned when you plug the logger back, to get the last data and reconstruct the filesystem in the case of a battery failure.

Temperature Logger 2.1: Schematics and basic BOM

The Altium files

The source code (based on Microchip Applications libraries -Device – Mass Storage – SD Card data logger- MPLABX)

I also made a program/debug adapter (especially useful for debugging):

USB-Temperature-Logger-Programming-tool

USB-Temperature-Logger-Programming-tool1This is the “office” version of my previous peg-adapter ;-)

A lot of people were asking me if I was selling these loggers. Unfortunately, no. The design and functionalities are sexy, but I don’t have the capacity to launch a production on my own. And if I had do make only a small batch, the price would be totally uncompetitive.

A big thanks for all the people who donated a little something to motivate me!! (or to help me be more ashamed of the lack of updates)

All the contents (except the parts of Microchip’s code in the source) are under the Creative commons license, Attribution – Share Alike – Non Commercial.

Creative Commons License
Simple temperature logger: v2.1 by Jean Wlodarski is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

Cheap, quick and dirty reflow oven

I got this cheap toaster in a “crap shop” for 11 Euros. It’s perfect for reflowing PCBs and small enough to fit in my lab:

Reflow-ToasterI tried to use only components I had at hand, including:

  • a DIP PIC 18F2450 (total overkill to control a heater, I know)
  • a relay from a timer AC socket
  • a small USB iPhone charger for the +5V supply
  • a K-thermocouple and a MAX6675 for the conversion (quite expensive chip, but very simple to use and I had it in a drawer)
  • a small LCD screen, two buttons and two LEDs

The PIC is running from the internal RC oscillator. Very slow, but enough for what it’s used for.

The relay comes from this timer I bought some time ago at Conrad:

It’s rated for 2000W, the PCB is easy to re-use and fuse protected. I added an opto-coupler, so the PIC and user interface are fully isolated from the 220V mains (also convenient for debugging). I thought about re-using the timer’s LCD and microcontroller, but it’s directly bonded on the upper PCB and difficult to hack.

I managed to squeeze everything into the toaster’s plastic flange. (Unfortunately the temperature can increase a lot inside, so I think I’ll move the electronics into a box, outside the toaster)

For now, I just have two functions:

Drying – keeps the oven at 100°C

Reflow – follows the standard leaded solder paste curve (2 minutes@150°C – 2minutes@200°C – 1minute@250°C)

The LEDs also act as switches to select between the two functions. I’m still looking for a good method to cut plastic in a clean way. It’s not so easy with my Dremel.

It took me more or less one day to build everything (I wasted some time for the LCD display control).

I’m only using the heating elements from the upper “toast hole”. The bottom stays cool enough for the toaster to sit on a table without the need of extra feet or thermal protection.

And of course, the oven works just fine for the small PCBs I have to solder!

Simple and cheap temperature logger: New update coming

I’m working on a new revision of the temperature logger: new PCB and new firmware. It’s easier to solder, as the resistors/caps are now 0603 instead of 0402 and the PIC package is now a SSOP28 (instead of QFN).
The sleep current is smaller than 10uA and below 1mA when measuring the temperature (plus a few mA every 20-or-so logs, when writing to EEPROM).

The EEPROM is a SST25WF080 (still 1,8V 8Mb), as the previous Atmel memory is not available any more.

Some 3D renderings of the PCB:

Simple and cheap temperature logger 2.1

The USB connector is a Multicomp MC32604, cheaper than the previous MCKUSBX-SMT2AP1S-W30. (I couldn’t find a suitable 3D model for the PCB rendering)

The ISCP connector for programming the firmware  is SMT but fits the Microchip’s ICD header:

The new firmware has functions for the new EEPROM, a low battery indication, more robust logging and USB update capabilities. Plus a lot of bugfixes and optimizations.

Now, to complete the firmware, I have to build at least one logger, which means ordering the PCB and the components. That’s why I added a “donate” button to this blog (on the top right side of the page, just under the title), especially I don’t earn any money with this blog and content is free (and will stay free, of course).

If my work helped you, if you find it interesting, if you want more articles and more projects, dropping a few coins will motivate me and help me to materialize all the projects waiting in my head. :)

Stay tuned for more!

Jean.

Interview!

I did an interview for Eeweb.com. You can read it here (and see the face behind this blog).

Right now, I don’t have much time to write new posts, as I found a job (I’m adapting my USB temperature logger for current and voltage logging). Very interesting project, with great people and for greater good :-).

I’ll write about it as soon as I have some time!!!

QJ1502C – 15V 2A Power supply review (Labornetzgerät Test) – Mastech HY1502D

Looking for a variable power supply for my bench, I stumbled upon this eBay offer: QJE branded 0..15V 0..2A lab power supply for 35 Euros, including shipping and taxes on German eBay (It looks very similar to the Mastech HY1502D on eBay.com, for $55).

I bought it form Komerci.de eBay shop. Ordered Sunday evening, it was sitting on my bench already on Tuesday.

There are some other models that do 0..30V 0..5A but they are more expensive (75-90 Euros) and bigger. As I’m usually not working with voltages over 12V, I thought 15V max would be enough. And for 35Euros more, I can buy a second one and have -15..+15V by putting the supplies in series.

The supply arrived in a well protected package, being itself in a cardboard, with the instructions and a pair of crocodile-banana wires.

The front panel has the essentials of a lab power supply: voltage and current knobs, two LEDs indicating the mode (Constant Current – Constant Voltage), two banana sockets (you can unscrew them to connect bare wires) an on/off switch (directly connected to the mains) and two LCD displays, for the voltage and current. A button to switch the supply between the CC and CV mode would be cool, but I guess you can’t ask that much for the price.

The labels are in German (Spannung: Voltage, Strom: Current). As I live in Berlin now, I better get used to it. :-)

The LCDs have a nice greenish backlight but unfortunately the angles of vision aren’t so great, the digits start to fade if the unit is 40cm on your right or your left side. But they’re ok if you put the unit on a shelf above your head.

(the backlight is actually easy to see even in daylight)

Another thing I noticed is how hard the knobs were to turn, the low efficiency of the green CV LED, the digital dot being hard to see and the poor LCD refresh rate. More on this later.

Let’s crack it open!

The case is made of metal except the front panel, which is plastic (OK-quality). Everything is held together by eight screws on the sides, plus four on the bottom, two for the front panel and two for the back one.

The design is quite standard: Control/display PCB on the front, power regulation PCB on the back and multi-tap transformer in the middle. There’s a lot of room left. My unit is the bottom-of-the-line one, so the manufacturer probably uses the same case for the more powerful models. Anyway, more room, less heat!

The cabling is clean, with double-insulated-heat-proofing for the mains (from the mains cable to the fuse and to the transformer, from the mains cable to the front power switch). Unfortunately, no double insulation from the power switch to the transformer.

Also, the transformer secondary cables insulation could have been cleaner.

The screws attaching the transformer, the heat sink and the ground lead have split washers. Good.

The front PCB is attached to the front panel by four screws and by the potentiometers. It looks like if it was bathed several times in flux. I think it’s the reason why the pots were so hard to turn. I cleaned them with a flux remover and they went back to normal once dry.

Apart from the flux-terrorism and that yellow wire for output transistor bias being directly soldered on a 1206 capacitor (come on, guys, what’s the point putting connectors for the other cables and doing that for that one wire?!), the PCB design is OK. I like the via-stitches and big planes to help the two voltage regulators dissipate heat.

[Edit: I just noticed there's a footprint for a connector for the yellow cable, but they decided to solder a capacitor parallel to it and the wire directly on the cap.]

As you can guess, the LCD displays are actually directly driven by the output voltage/current, not by the pots setting. Which means that the unit goes to 16,3V and 2,1A. It also means that what you read on the LCDs is what you’re getting on the output.

This task is done by two identical ICs, the CS7106GN, an obscure piece of silicon, [As Bernhard D. commented: The CS7106GN isn’t really “a obscure piece of silicon, designed and made in china”. It is a chinese copy of the Intersil ICL7106, available since roundabout 1978.] designed and made in china (datasheet here, Chinese-only). It’s basically a voltmeter/LCD driver:

An interesting thing is the oscillator circuit. I said the LCDs’ refresh rate was poor. In the datasheet, the default capacitor value on OSC3 is 100pF. I replaced it with a 33pF and… Success! the refresh rate is now more than acceptable, without any precision/resolution loss.

I also replaced the green CV led by a more efficient one.

The voltage/current command is entirely analog (the two dual op-amps on the front PCB). It would be interesting to replace the front panel potentiometers by digital encoders commanding two digital potentiometers driven by a microcontroller. Add some USB/Serial capability, two ADC and voilà, you have a remote-controlled lab power supply. Quite tempting!

The output banana connectors are mounted on a PCB with a common mode filter and a protection diode, plus the current shunt. Unfortunately, they’re not bolted but only soldered, as are the output cables:

The voltage/current regulation is made by a TIP3055 power NPN transistor on the other PCB. It’s rated for 90W/70V/15A, so it won’t be screaming with the 15V/2A it’s asked for. The heatsink is also generous (passive cooling only):

The transistor is actually mounted on the other side of the PCB ad directly bolted to the heatsink, with a thermal pad. Simple-but-ok construction.

(The other hole is to hold the PCB. There’s a plastic spacer between the heatsink and the PCB. The transistor mounting hole is isolated too)

Even if this second PCB looks way cheaper than the front one, the manufacturer make the effort of glueing the filtering cap. The rectifier diodes could be further from the relay due to heat, but I’m not sure they dissipate so much power.

Now, what about the performances?

I compared the LCD readings with the ones on my Fluke 79III (calibrated) multimeter. They’re within 50mV range. The output voltage ripple is below 5mV for all current/voltage combinations.

The unit is within specs, before or after warming up. The relay clicks-in between 4.2V and 4.3V (to switch in the transformer second tap) without any peaks on the output voltage.

The start-up voltage ramp is nice, without any overshooting (and I tried several times, with several voltage settings):

Conclusion:

I must say I’m very surprised by the quality and performance vs. price ratio of this lab power supply. For 35 Euros, I’m not sure you can get even the case from Farnell. Here, you get a very nice 0..15V 0..2A power supply, with digital display, good accuracy and enough for most of the everyday needs. Plus, it begs to be modded!

Sense of humour in datasheet.

I wasn’t expecting to find humour in one of Microchip’s Application Notes, especially one about 48 applications with the CTMU. (AN1375, “See what you can do with the CTMU”):

Ok, not as great as “The Polish OpAmp”, from National Semiconductor, but it’s always nice to find something like that nowadays!