Homebrew, open source, repurposed, hacked, software defined, open hardware

Monday, 30 May 2011

Finishing off the SDR Cube transceiver

I finally got around to starting the final bits of the SDR cube transceiver I started a while back. It's a self contained SDR (software defined radio) transceiver made from a kit.

see: http://www.sdr-cube.com

I have already built the Softrock 6.3 which mounts inside the SDR cube, and now need to make the transmit power amplifier (TXPA)) board, and the low pass filter (LPF) board, and the receive amplifier (RXPA) board.

I have started with the TXPA board, and first of all, the surface mount components.

Surface mount soldering used to be a bit scary, but this technique using a sub $40 hot plate (skillet to those of you abroad) and solder paste, and a simple 3mm (1/8 inch) aluminium heat transfer and lift off jig makes it a 10 minute process to solder the whole board.

You can see the full write up of the settings used and the process at my local amateur radio club - Adelaide Hills Amateur Radio Society -  website:


I have done many runs with this hotplate starting at room temperature, and have found with the help of thermocouple readings that starting at ambient on setting 4 gives you a really good approximation of the recommended JEDEC heating profile if you turn it off at 250 seconds, then allow the thermal inertia to continue for another 30 seconds, and then lift off the board at 280 seconds.

A commonly asked question is why not leave the whole lot to cool, and skip the lift off. The answer is that the thermal mass of the hotplate is too great, and will cook the board and components after 280 seconds have elapsed, but lifting off gives you the ideal cooling down profile.

Some people use small toaster ovens, but these were more expensive when I went into Cunningham's warehouse, plus removing the hot board with molten solder is harder with a toaster oven, and some people report overheating plastic components with the heat coming from on top of the board.

First, you apply the solder paste with a toothpick or needle:

Then you place the components - tweezers work well, others use vacuum pickup devices bodged together with pen barrels, needles and aquarium pumps:

Then you turn on the hotplate. This is a cheap ~AUD$40 Tiffany branded hotplate which follows the recommended JEDEC heating profile on setting 4, and is then turned off at 250 seconds, and then with the boards lifted off at 280 seconds to cool, it works a treat.

The hotplate is unplugged at 250 seconds, and at 280 seconds, the boards are gently lifted with the simple jig made up of a 3mm (1/8 inch) aluminium carrier plate, and some support arms with a handle at the left and a fulcrum at the right. The jig can be gently lifted up and supported to get the boards away from the heat source.

The carrier plate spreads the heat nicely, allows the boards with the still molten solder to be gently lifted without dislodging the components, and allows the heat source to then be removed after it has been chocked, in this case, with the nearest thing handy - a tissue box.

After things have cooled enough to allow the boards to be handled, you can move onto the through hole components.

So, in summary, surface mount soldering need not be expensive, difficult or scary for the newbie. It really can be this quick, easy and cheap to do at home.


specs for the hotplate / skillet used for the SMD reflow. The unit weighs 2.4kg, and apart from the hot plate with embedded element, there is little else to it, other than the sheet metal enclosure, knob, and plastic feet. It is nominally rated at 1500W, and appears to use a bimetallic switch for heat regulation. I suspect my setting 4 is actually "always on" for the 250 second runs. The hot plate portion is 190mm round, and quite magnetic, suggesting that it is iron, as opposed to cast aluminium.

Friday, 27 May 2011

USB sniffer made from a USB power injector kit

I liked the idea of a USB bus sniffer that could be interposed between the computer and the peripheral, as described in a recent silicon chip magazine. I thought it might come in useful for anticipated Arduino hacking in the near future.

I thought about what was needed to make a board to fit the USB A and B connectors, and then having to source the connectors from dead hardware like a discarded printer, and then find a suitable enclosure which would allow USB port accessibility. Hmmm. I then saw a USB power injector kit on sale at Altronics for AUD$12



well, this was 90% of the work already done, and all that was needed were some banana posts for the D+, D-, 5V and Ground terminals, and as a bonus, it could inject power for whatever peripheral I was working on.

An extra switch seemed worthwhile to switch between the PC 5V USB supply and external plugpack 5V power injection.

Here's the modified circuit, with due deference to Silicon Chip's original circuit.

How the board comes:

How the board comes bottom side view. Not a lot of space for four connectors, but just enough, it turns out:

Holes were drilled where space was kind of available for the banana post stems for the D+, D-, 5V and Ground connections, and an extra hole to allow a 10uF tantalum to sit out of the way of the Ground banana post:

The box lid was drilled using the circuit board as a template to match the banana post locations, and for the DPDT miniature switch. When finally assembled, the red banana post does not have the nut attached, as it would likely short out the LM7805 heat sink:

The lid was then put together followed by the board trackwork being cut to allow the external 5V supply to be switched in and out, and to allow the banana posts to be connected, and to keep components which would get in the way to be re-routed:

The board was then populated with components on the top side, and the DPDT switch was then wired to allow pass through for the USB B -> A power, or via the power injection circuit. One of the tantalum cap legs had to go into one of the new holes drilled to keep it out of the way of the Ground banana post, and two resistors had to go under the board to keep them out of the way of the D+ and D- banana posts:

The underside of the board was finished off, and the 5V banana post got its own PCB island just north of the LM7805 heat sink for the wiring from the switch, which then went on to the Type A USB connector. Hint for young players - the stems of the banana posts wet very easily with solder if you spin some 180 grit sandpaper or similar around them to get through the oxide layer on the electroplating before you solder to them. Scraping with something sharp will also do the trick:

Finally assembled:

The switch allows selection of the 5V source, and the red and black banana terminals gave 5.15V from the netbook and 5.01V from the internal 7805 regulator when running off an external plugpack.

Green and white are D+ and D-.

The original article describing the bus sniffer showed a 1 ohm resistor that could be placed in series or shorted with a jumper to allow measurement of the current being drawn by the device. This seemed a little superfluous if a power supply with a current readout and/or current limiting is used for external powering of the USB device with this unit, but a jumpered resistor could be shoehorned into the box if one were really keen.

So, in conclusion, if you want to build a USB bus sniffer, a power injector my be an easy way to do it, with the added bonus of not frying your USB host if things go a bit haywire with power requirements.

I suppose I should get my hands on an arduino now.

Hot off the press - cross platform Microchip IDE

Ooh my, just when I was feeling guiltier and guiltier for harboring ongoing predilections for PIC microcontrollers even though there was no decent linux/OSS toolchain, it seems Microchip have come to their senses and released a cross platform IDE.

I came across this while checking out the newly released dsPIC based arduino shield and arduino IDE compatible chipKIT Uno32.



Joy of joys. This was one of the  few remaining reasons to have a windows partition....

I reckon the dsPICs have awesome potential for SDR applications, such as beaconing/WSPR/QRSS. Hmmm, I really should finish off my SDR cube now and then play with the code a bit.

Finishing the signal tracer

Like a lot of amateur radio operators, I have quite a few partly finished projects lying around, usually at the point of being a working circuit board, but not boxed up and labeled.

Waiting for the amoxycillin and clavulanic acid to kick in for the head cold, and waiting for the batteries and hardware for the roller shutter mods to arrive,  I avoided the urge to start a new project, and thought I'd actually finish one for a change.

I bought a signal injector and tracer kit from oatley electronics a while back.


It is very similar/essentially the same as the published silicon chip design:


A 555 putting out an audio signal at a few KHz is made to sweep up and down in frequency by another 555 which is doing the frequency modulation, and this becomes the signal for injection into your cable with many harmonics.

The tracer has some front end amplification with the 2N5484 followed by a transistor stage which achieves some detection as well.

I thought why not add a simple audio tracer function and complicate things by adding a 3 pole 3 position switch to take care of power, AF and RF input routing, and LM386 input routing, and add a potentiometer for AF gain.

The LM386 input is hi-jacked for the AF signal tracing, and the RF input stage is only powered up when the input BNC is routing the signal through the RF front end.

So, the kit gets to do double duty as an RF signal tracer and an AF signal tracer.

The photo shows the innards of the tracer, with the signal routing and power routing on the rotary switch.

The dividers making up the 9V battery compartment were made with tin snips and some spare ABS panel from a lexmark printer found in a dumpster. I prefer to use an external power supply for gear that is not used frequently, and added the switched DC barrel connector socket, as well as an external 8 ohm audio jack.

All done. I won't lose the screws for the lid now that the lid can be left on permanently.

I've now made it a habit to label the power connector so I don't have to dig up the specs a year later when I've forgotten what it needs for power.

Saturday, 21 May 2011

The roller shutter controller

Here are some photos of the roller shutter controllers.
A torx security screwdriver and you're off and away.
Note the 12 x AA x 1.2V NiMH battery pack.
The battery pack is a nominal 14.4V 1500mAH

These battery packs get very hot when charging....
This might explain why so many have died....
I rang the factory, which is local, but they never
called back about replacement battery packs.
Oh well, that has motivated all this. Hopefully this will
help others confronting this problem, like VK5FDGW.
The unregulated 28V DC wall charger did not impress
me either.

I have seen replacement battery packs on e-bay for
about AUD$80
I have seen AA 1.2V NiMH tagged cells for AUD$4 in
quantity, which are 2000mAH.
So, I could buy a new battery pack, for AUD$80, and
wait for it to die again...
Or, I could make a battery pack, not a simple thing,
as it has to shoe horn back into the controller and I'd
need to solder or spot weld 11 pairs of tags, and it
would cost at least AUD$48 for the AA cells, and then
having done this, wait for it to die again.

Five dead controller battery packs starts to add up to
real money.

So, the next step was to try the trusty bench power supply.

The shutters are fairly large, up to 5 m^2 per roller shutter, which
was the maximum allowed at the time we bought them.
I removed the battery pack, and attached the leads to the socket
pins which the battery pack attaches to. The battery leads are
red and black, which should be observed when attaching an
external power supply.
As the roller shutter starts to go up, it seems in excess of 2.5A are
drawn at roughly 14V DC.
The controller refuses to work if the input voltage is in excess of
19V or so.
The next step was to try an SLA battery, plugged into the controller.
The following battery is a 1.3AH 12V battery which sells for
AUD$18 in quantity.

The battery is being topped up here, after playing with the roller
shutters. It needs needs no more than 130mA to top it up, for
constant voltage charging.
The battery is adequate for lifting and lowering the roller shutters.
The roller shutters only need 1.5A or less, when being lowered.

So, five AUD$18 batteries is sounding much more reasonable.

I suspect I could replace the controllers with simple switches
to move the shutters up and down, but I reckon a simple fly
lead to the nearby (currently) blank wall plate for power will
allow me to hide the battery in the wall further down. There is
a spare cat5 cable behind the blank wall plate which will be
used to float charge the battery daily.

SLA charging is easy, and I will knock up a current limited
fixed voltage charging circuit next, delivering about 130mA.
This should keep the batteries happy and healthy for many
years, and should be more reliable than the NiMH batteries.

The roller shutters are available with AC powered controllers
but we are in a bushfire area and want them to work when
AC power is not available. Also, we are on off grid solar and
don't want phantom loads overnight.

Some inspection of the circuit board revealed some power
conditioning for the unregulated charger input, dropping it to
about 15V with a switched mode circuit, which charges the
onboard battery via a diode at around 160mA.
After this diode is the common 15V bus.
The 15V then moves on to a high efficiency switched mode
power supply chip LP2951 which steps it down to around 5V
for the ATMEGA48.
There is space on the circuit board and some antenna
trackwork for 433MHz receiver bits and pieces for the
remotely actuated version which is sold.
There is also the driver circuitry for the roller shutter
motors, and some current sensing for the roller shutter
current, and some test points.

One down side of using an external SLA battery is that
the controller decides that the battery needs charging, and
it seems the ATMEGA48 has some kind of logic for starting
and completing charging, however broken. The effect of
this is an infrequent, regular flash of a red LED, visible from
the front of the controller.

Feeling too lazy to reverse engineer the ATMEGA firmware,
I plan to cut the single track going to the red LED. Ignorance
will be bliss.

The other thing to do will be splicing in some wiring that will
also go down the fly lead which will allow the controller to be told
to open or shut the roller shutter remotely, via the spare cat5
cable conductors. There will be plenty of space in the controller
without a battery pack if another microcontroller is needed.

Then, just add a web interface and an android phone....

Hmm, I wonder how the warranty will be affected....

First Post

Well, I needed somewhere to put my random hacks and

So, here it is.

Coming soon... how to use cheap SLA batteries with
OZroll (TM) roller shutter controllers... instead of the
expensive NiMH battery packs which die so easily....

This will probably be a theme of this blog.... fixing stuff
the manufacturer should have done right the first time,
keeping stuff out of landfill, hacking stuff together with
stuff found on the side of the road, using appropriate
technology, and pondering how best to apply the
the laws of thermodynamics to subversive ends ....

To quote Sheldon Cooper:

the physics is theoretical, but the fun is real.....