HUB75 RGB LED matrices with Arduino

juuli 29th, 2014
by jaanus
Cheap HUB75 RGB matrix working

Cheap HUB75 RGB matrix working

Everyone likes LEDs. I like when I have a bunch of them. So one day I realised that I have about 15 big 32x16 RGB LED matrices in my lab. They are cheaper versions of Adafruit's led matrixes. Both matrices use standard HUB75 pinout. The pinout is same, LED count is the same, but display doesn't work - it is wired differently inside.

Driving matrices

Most simple way to do a led matrix is to drive low side columns with sinking driver chips and rows with high side mosfets. When you have bigger display - let's say 24 driver chips in total, then usually you will make multiple parallel lines of data to clock information faster.

HUB75

HUB75 is a standard interface to control matrices like that. It has binary inputs for mosfet control: A, B, C and D. So you can have up to 16 rows. Also, you have 6 data buses: R1, G1, B1, R2, G2, B2. Now, to control a matrix you have to know two things: how many virtual rows and columns does your matrix have and how are they mapped with reality.

Backside of my LED matrix, 24 drivers are visible.

Backside of my LED matrix, 24 drivers are visible.

Differences from device to device

The Adafruit matrix has 12 driver chips and 8 rows controlled by mosfets. Mine have 24 driver chips and 4 rows. Also, Adafruit's one seems to be mapped quite straightforward way. Mine in the other hand.. rows are separated to eight banks that are all in different directions. Still - no problem. Mark Laane, a programmer in my lab, sat down with the matrix and soon we had a working library. You can find it from here:

https://github.com/zidik/LedMatrix16x32-Alternative

Arduino Micro soldered to HUB75

Arduino Micro soldered to HUB75

Electrical wiring

I soldered my matrices directly to Arduino Micros. Since the pinout is slightly different from Uno, the connection diagram got hurt a bit. This library works with following connections:

HUB75 Connect to On Micro
R1 PB2 MOSI
G1 PB3 MISO
B1 PB4 8
GND GND
R2 PB5 9
G2 PB6 10
B2 PB7 11
GND GND
A A0
B A1
C A2
D GND
CLK A3
LAT A4
OE A5
GND GND

 

Posted in Small projects, Soft | Comments (0)

32 channel mains lamp controller

mai 21st, 2014
by jaanus
4 channel stackable thyristor board

4 channel stackable thyristor board

I needed a computer controllable 32 channel light dimmer for an art installation. After looking around a bit I found out that there isn't even a Arduino shield for the work. So I made a quick 4 channel stackable board to control lights.

The board uses SHARP thyristor based solid state relays to switch mains voltage. As normal with thyristors - all the outputs can be used as dimmers through zero-crossing detection. All outputs are able to handle 0.9 A / 200 W. We connected 40 W incandescent light bulbs to it but you can control whatever with it - lights, electronics, computers, motors etc.

The end device has Arduino as a controller, so all the lights can be switched from computer over USB. And since all the outputs are optically isolated from controller, the USB side is quite safe even in error situations. Also the Arduino can be reprogrammed for any preset pattern.

Get the controller source code from github: https://github.com/jaanuskalde/light-controller

Or buy it from my open source webshophttp://tech-thing.org/usb-controller-light-dimmer/

16 channels of mains switch

16 channels of mains switch

32 channel lamp dimmer overview

32 channel lamp dimmer overview

Back side of the device. USB and manual.

Back side of the device. USB and manual.

Posted in Small projects | Comments (2)

Multicode transmitter

mai 19th, 2014
by jaanus
Satel multicode transmitter

Satel multicode transmitter

I got my hands on a broken Satel OY multicode transmitter. It is an transmitter used to get information from remote sites - alarm codes, telemetry or sensor values. You can attache it to your pump or ground station and it sends a message up to 30 km if something is wrong. It puts up to 4 W of output power to VHF band 152 MHz in FSK modulation. As alarm systems go - it also had a place for backup battery.

This device is designed and produced in the end of nineties and it can be seen from the build. Old chips and packages.

The device itself is screwed in a thick aluminium box for weatherproofing, RF shielding and mechanical rigidity. Input power and signals come from DB15 connector and all go through low pass filters for protection. It has to survive the scariest test ever - the user! The brain of the thing is socketed Atmel TS87C51RB2 in a PLCC44 package. It is a device before flash memory - only single programmable!

Overview of transmitter

Overview of transmitter

From RF section we don't find fancy transceiver chips. Frequency synthesise is done by temperature controller temperature oscillator in a separate metal can. Modulating multicode is generated by Motorola MC14515 PLL frequency synthesizer. Bunch of analog RF circuitry filled by RF inductors does the modulation and matching. The output is amplified by BLT50 Power amplifier that is used out datasheet frequencies. Do your own datasheet - typical for RF power stuff. They don't use air core inductors, so they lose a bit of efficiency, but since it is externally powered they don't care. Also TLC542 ADC is used to get some feedback from RF front end.

Back side of the PCB

Back side of the PCB

Power amplifier and insides of a TCXO

Power amplifier and insides of a TCXO

Posted in RF, Teardowns and reviews | Comments (0)

Laserworld CS-500RGY

veebruar 28th, 2014
by jaanus
Laser projector, working

Laser projector, working

I got my hands on a Laserworld CS-500RGY laser projector. This is the smallest 500 mW one. It is a device that has three laser sources (red, red and green) and mirrors for moving laser pointer. It can be controlled by sound, DMX512 or ILDA interface. So, lets tear it down.

Case is really rugged and strong, made to last. Also has two fans for forced air cooling. Most of the insides is empty, they use the same chassis up to 2 W RGB projectors. Electronics is really modular and all through hole assembly. All what you would expect from low volume device and more than 10 year old company.

The laser assembly has two beam splitters that combine three laser sources into one. They two motors with feedback are used to move mirrors into correct angle.

Laserworld laser insides

Laserworld laser insides

Laser assembly, two small red lasers and one big green.

Laser assembly, two small red lasers and one big green.

Mirror assembly with two stepper motors.

Mirror assembly with two stepper motors.

Main processor with firmware sticker

Main processor with firmware sticker

Posted in Teardowns and reviews | Comments (1)

Contract engineering

veebruar 20th, 2014
by jaanus

I have done contract electrical engineering for ages. Previously mostly for university and friends, but as time went forward, more and more professionally for companies. As I also got my own lab and couple of employees - it was time to go official. So I got involved with couple of companies.

Tech-thing OÜ - electrical design and small scale manufacturing. We have capability to design and prototype wide area of devices - from small LED devices to big motor controllers and RF circuits.

Crystalspace OÜ - nanosatellite subsystems and components.  We specialize into making small satellite components, like power supplies, attitude determination and communication systems. Also mechanical components like frames and reaction wheels. And finally - whole small satellites.

Posted in Other | Comments (0)

Matching rf amplifier: Smith chart matching

jaanuar 23rd, 2014
by jaanus
linSmith with PI matching circuit

linSmith with PI matching circuit

I have to match 7.799 Ω+1.3158j to 50 Ω load with PI filter at 430 MHz. My advisor's advice - use pen and paper and Smith chart. But since I'm determined not to do maths on paper ever again (we have computing machines available now) then I started to search other ways out. So I read a tutorial on Impedance Matching and The Yin-Yang of Matching, really great stuff.

Then I found program called linSmith. Runs natively on linux, but requires compiling. User interface is quite good and no user manual is needed. I just typed in working frequency and starting complex impedance. Next I put in PI filter components with approximate values. It started showing all values on Smith chart. Little bit of playing around with sliders to adjust values. After couple of minutes I had values for my filter that matched impedance well and was made out of readily available components.

Next step is testing the calculated values on real circuit board. Real board and components have parasitic elements. The final values will be determined by trial and error, but the calculators give very good starting point.

Posted in RF | Comments (0)

MIMP, Advanced Design Studio, scikit-rf

november 5th, 2013
by jaanus

I was searching for a program to match RF circuits. I already calculated input complex impedance and choose pi filter as topology.

First I looked Motorola Impedance Matching Program. It is really old program, runs in Dosbox and is quite awful. User interface is manageable after reading the manual couple of times. Got the filter values from the program, but I'm not sure in these since I'm not sure I used it correctly. But in its free and cross platform so, why not use it.

I also tried Agilent Advanced Design Studio, but yea, it is meant for full time RF engineers. It looks like it can do everything. Usability is almost okay, feels inconvenient like ltspice.

Next I tried to simulate the circuit with scikit-rf. Importing the network worked fine, but the easy part ended there. To make components I first needed to make Media. There was no lumped element Media, so I took the one easiest to use - Freespace. Also the connections don't sound really correct.

#Program accepts one argument - C1 value in picoFarads of PI filter. 
#It outputs transistor output impedance (calculated from amp.s1p file) 
#and a graph showing preferred PI filter component values.
import matplotlib.pyplot as plt
from pylab import *
plt.ion()

import skrf as rf
rf.pico = 1e-12

import sys

#amp that we are matching only S22
amp = rf.Network('amp.s1p')

print amp.z

#we need media to make components. weird
media = rf.media.Freespace(amp.frequency)

def get_db(C1, L, C2):
   #pi filter begin
   C1 = media.shunt_capacitor(C1*rf.pico);
   L = media.inductor(L*rf.nano)
   C2 = media.shunt_capacitor(C2*rf.pico);

   filter = rf.connect(rf.connect(rf.connect(amp,0,C1,0),0,L,0),0,C2,0)
   return filter.s_mag[0][0][0]

print get_db(10,22,7)

out = []
for L in range(1,15*3,3):
   out.append([])
   for C2 in range(1,15*2,2):
      out[-1].append(get_db(int(sys.argv[1]),L,C2))

#raw_input()
#print out
figure()
title('Pi matching network, C1 = '+sys.argv[1]+' pF')
imshow(out)
xlabel('C2 value [pF]')
ylabel('L value [nH]')
xticks(range(15), range(1,15*2,2))
yticks(range(15), range(1,15*3,3))
cbar = colorbar()
cbar.set_label('Return Loss Magnitude')
grid(False)

show()

raw_input()
PI filter values in respect of output reflected power.

PI filter values in respect of output reflected power.

And this program provides graph you can see on the right. Really nice graph what in theory should show right values. I like how I can look at the graph and pick values that exists in the shop and see how effective filter would be. But again, I can't verify these values on other tools so there is probably small miscalculation in my code.

Posted in Teardowns and reviews | Comments (3)

Matching rf amplifier: calculating complex impedance

jaanuar 23rd, 2014
by jaanus

I'm building a small 430 MHz  1 W RF amplifier to get some practical knowledge about RF design. Choosing components and making the PCBs was walk in the park. But suddenly my instructor said that I have to match my amplifier with next stage.  It is weird, because I thought that RF amplifier meant that output would be 50 Ω, but no, it is something totally random.

So, my amplifier TQP7M9105 has page with S parameters. S parameters are parameters that describe RF components working in a 50 Ω environment. In our case S22 is what we want. 22 mean that it is second port reflections to second port aka output information. S22 at 400 MHz is -2.73 dB 176.91 degrees. This is - connecting output directly to 50 Ω output you get attenuation of 2.73 dB and phase shift of 176.91.

To calculate complex output impedance I used scikit-rf python library, because I couldn't find any online calculators doing the same job. Input was fed from  Touchstone SnP Format file type, because this was the only way I could think of to convert dB form to rectangular form:

# MHz S DB R50
400 -2.73 176.91

And code itself was:

import skrf as rf
amp = rf.Network('amp.s1p')
print amp.z

So, my amplifier output impedance @400 MHz should be 7.799Ω+1.3158j. Quick check from mismatch calculator confirmed my results. Next I used PI-match impedance matching calculator to calculate necessary values. Got some answers, probably will use other methods to check if they are correct.

Posted in RF | Comments (1)

Buck-boost converter from LT3791-1

oktoober 22nd, 2013
by jaanus
Finished prototype, some mosfets and big inductor.

Finished prototype, some mosfets and big inductor.

I'm building quite high power (for me) buck-boost converter for a friend. It takes in 12-45 V and has to output regulated 24 V. Total output power has to be more than 300 W. I don't understand switching regulators well enough to build more than 100 W regulators from 555 timer (that is basically how your computer power supply is built). Just too much phase shifting and output oscillations and whatever else to take into account. You know, the things you learn in electronics classes (which there was none in my school).

LT3791-1 in the middle of a debugging session.

LT3791-1 in the middle of a debugging session.

So I took the highest power buck-boost controller I could find - LT3791-1. It satisfied all my specifications so I calculated what parts would I need to make a 300 W board out of it. After ordering stuff and soldering it together it looked awesome. But after some playing around I couldn't get it to boost more than 100W, buck worked well but boost didn't. After lots of debugging and bunch of fried chips I finally figured out that the MOSFET drivers are too weak. My big and high power mosfets didn't even get warm at 300W output, but the chips internal voltage regulator fried all the time.

So, lessons learned from high power:

  • Every watt adds problems to MOSFET driving
  • Don't over specify parts three times

Next prototypes will be smaller and there will be several of them in parallel. Maybe some pictures soon.

Posted in Small projects | Comments (9)

Aalto-1 photos

september 27th, 2013
by jaanus

I have been visiting finnish Aalto-1 satellite project a couple of times. I am building half of one of their experiments - motor control board for electric plasma brake. Took bunch of cool pictures of their technology. Enjoy.

Mock-up satellite for exhibitions. Really good for overview.

Mock-up satellite for exhibitions. Really good for overview.

LM75 temperature sensor on the outside of the satellite.

LM75 temperature sensor on the outside of the satellite.

Solar cells are soldered to the PCB, it gave some trouble in thermal vacuum tests.

Solar cells are soldered to the PCB, it gave some trouble in thermal vacuum tests.

Prototype of Aalto-1 on board computer. Two cold redundant AT91RM9200 ARM processors running linux. And small MSP420 FRAM microcontroller that switches between them.

Prototype of Aalto-1 on board computer. Two cold redundant AT91RM9200 ARM processors running linux. And small MSP420 FRAM microcontroller that switches between them.

Bottom of on-board computer. Battery for real time clock and some memory.

Bottom of on-board computer. Battery for real time clock and some memory.

S-band downlink and GPS system. On the bottom there are: S-band tranciever, distributed element filters, power ampliffier and some more filters. On the top there is GPS module with antenna connector.

S-band downlink and GPS system. On the bottom there are: S-band tranciever, distributed element filters, power ampliffier and some more filters. On the top there is GPS module with antenna connector.

Local flatsat, really useful for satellite testing if it works.

Local flatsat, really useful for satellite testing if it works.

Open antenna setup. It consists of two 70cm dipole antennas. Elements are connected with UMC connectors and antenna block with MCX.

Open antenna setup. It consists of two 70cm dipole antennas. Elements are connected with UMC connectors and antenna block with MCX.

Antenna relase mechanism. Resistors for burning the wire and switches to detect the release.

Antenna relase mechanism. Resistors for burning the wire and switches to detect the release.

What I want to find from every lab: bunch of multimeters on a stack of documentation.

What I want to find from every lab: bunch of multimeters on a stack of documentation.

Prototype electrical power system for next satellite. Looks like classical EagleCAD work.

Prototype electrical power system for next satellite. Looks like classical EagleCAD work.

Another power system prototype.

Another power system prototype.

The side of the satellite. Solar cells, connecting PCB and strong machined side panel.

The side of the satellite. Solar cells, connecting PCB and strong machined side panel.

Posted in Space | Comments (0)

New lab

september 12th, 2013
by jaanus
Old lab in my room.

Old lab in my room.

My old lab was in the corner of my dorm room and as projects proceeded I needed a bigger lab. So, I got one. I teamed up with couple of my friends and we got 80m2 of space in nearly industrial building. It is nice to have room big enough to have 7m Yagi antenna indoors. In the same room there is EDM OÜ making small CNC machines and soon, couple of more startups.

New lab area, with more room.

New lab area, with more room.

Mechanics room with some machines and antenna.

Mechanics room with some machines and antenna.

Posted in Small projects | Comments (2)

Bicolor led cube

august 29th, 2013
by jaanus
Bicolor led cube, displaying red characters.

Bicolor led cube, displaying red characters.

I needed a bicolor LED cube, so I designed one. One coloured cubes are useful only as toys so bicolor one seemed like the easiest to make. I used Atmega8u2 to control two TLC5926 and high side switching was done with four small mosfets. As a bonus feature I used NCP3170 to convert USB 5V to 2.2V more suitable for red and green LEDs. Using a switching regulator let me use power from USB more efficiently.

Bottom side of LED controller board.

Bottom side of LED controller board.

My second led cube was much more ambitious - 6x6x4 RGB led cube. I planned to use one big Atmaga and charlieplex all the pins. I did the easy part - calculations, designing the system, routed and soldered the circuit board. Then I faced with the killer part - soldering 144 small surface mount three color LEDs to thin wires to form a cube. I tried couple of different racks but it was too time consuming to do even one. Some day when I think of a better way I will build a dozen, but for now it goes on my Out of Development wall.

LED cube controller.

LED cube controller.

Posted in Small projects | Comments (0)

AMSAT-UK Colloquium

august 5th, 2013
by jaanus
High end camera system for cubesat. Three temperature compensated cameras, beefy FPGA, radiation sensors and bunch of flex-rigid cabling.

High end camera system for cubesat. Three temperature compensated cameras, beefy FPGA, radiation sensors and bunch of flex-rigid cabling.

So I got the opportunity to visit AMSAT-UK  Colloquium. What is that anyway? Well - Radio Amateur Satellite Corporation UK edition's meetup.

ISIS VHF/UHF radio system. Notice the weird soldering of crystals and resonators.

ISIS VHF/UHF radio system. Notice the weird soldering of crystals and resonators.

On the first day there was a bring your own board meetup. So we took about all of the ESTCube-1 PCB and threw them on the table and went off to talk with other people. It was really fun and I took a lot of pictures of other people's work. From that I learned that many people have the same problems as us. System engineering problems, internal communication protocols and so on.

There was a bunch of talks about well, amateur radio satellites. European Space Agency guy was talking about their workflow (which made me doubt in them a bit more) and then about their projects (which made me to like them again). QB50 guys were talking about behind the scenes and future of this project. I got more confirmation that system engineering is awesomely hard. So I want to do it even more.

We got a tour in the Surrey University space center and Surrey Satellite Technology LTD headquaters and could see in their cleanrooms. They had more cleanroom soldering places as whole Tartu has normal ones..

But most importanly - I meet up with a lot of cool people. If everything goes well then I will be involved in some ESA projects soon.

NB. And I got to see the PCBSat, wee!

Pretty and small GPS for space. Surrey SGR-05. Normal GPS algorithms are made for using ON the planet so you need you own. Also if you go further than GPS satellites they you can't hear them very well. Antennas are directional towards earth.

Pretty and small GPS for space. Surrey SGR-05. Normal GPS algorithms are made for using ON the planet so you need you own. Also if you go further than GPS satellites they you can't hear them very well. Antennas are directional towards earth.

PCBSat! 1/4 U Cubesat. The cutest thing ever!

PCBSat! 1/4 U Cubesat. The cutest thing ever!

PCBSat internals. Not so impressive but basically as good as half of cubesats.

PCBSat internals. Not so impressive but basically as good as half of cubesats.

Posted in Space | Comments (0)

Tiny reflow oven controller

juuli 22nd, 2013
by jaanus

I looked at commercial reflow ovens and saw that they are expensive. That is a pity, because the hardware in them doesn't cost anything (Yea, I know, the development costs).

Prototype of reflow oven controller

Prototype of reflow oven controller

So I made a board controller that allows you to temperature control anything with minimum components. It has 4A TRIAC to control the heater, temperature sensor and attiny13 to control the heating. Also a red button, LED and on line regulator. The BOM cost was about 6$ in single quantities from Farnell.

Debugging the prototype was quite "fun". On line regulator meant that my ground was actually quite close to line voltages, so the probing was pretty dangerous. To use oscilloscope I used one channel as a virtual ground and divided two channels with math.

I got the regulator and zero volt crossover detection working but the TRIAC drive circuitry didn't work. The code was finally working, but I managed to blow the TRIAC somehow. I used small pulse after each zero volt crossover to turn on the TRIAC for the next half cycle. It brought the projects energy consumption quite low, only couple of mA. This allowed me to use quite small (100 nF) mains rated capacitor for the regulator.

Board layout with high voltage area clearly visible.

Board layout with high voltage area clearly visible.

At some point I decided to stop this project. Debugging it was too dangerous and I had made couple of bad design decisions. Like believing screw terminal over 300 V rating. Line voltages and 3.5 mm pitch screw terminals shouldn't go together.

Get the source files from GitHub

The schematic (PDF)

Since I still needed a reflow oven: I took a sandwich grill, added a thermistor, a small 5V relay and simple atmega32u4 devboard. Half an hour of coding later and now I have a reflow oven. PID controllers and thermal profiles are overrated, everything works perfectly with "go to 220 degrees then shut down" logic.

Final oven assembly. Thermal glue is holding the thermistor and relay is soldered on the wires.

Final oven assembly. Thermal glue is holding the thermistor and relay is soldered on the wires.

Posted in Small projects | Comments (3)

Kicad gerber renamer

juuli 15th, 2013
by jaanus

School is over, I'm finally able to do some work again.

I had some PCB orders to make. So, script I have been wanting to make for a long time - KiCad gerber renamer. It is a shell script that takes gerber files that KiCAD produces and renames them to match ITEAD or Seeedstudio file requirements. Really handy. Works with multiple versions of KiCAD (daily and older).

GET IT!

Posted in Soft | Comments (0)

Saike 898D teardown and upgrade

juuli 8th, 2013
by jaanus
Saike 898D soldering station

Saike 898D soldering station

So I tore town my hot air station another day. It was bugging me that it restarted every time my refrigerator turned on. Probably a problem with not enough (if any) filtering.

Couple of screws later and it popped open. First impression - it is dirt cheap. Well, it is THE cheapest hot air and soldering iron station but wow.. It has a big transformer in its core. Transformer powers board with microcontroller, that controls the screen and buttons. Power for the soldering iron comes from different winding and is controlled by thyristor through a opto-isolator.

Main PCB and cabling of soldering iron

Main PCB and cabling of soldering iron

Some critisism: Single layer paper PCB, insides is a cabling nightmare. Everything is through hole, because you know - workforce is free.. It didn't even have a 7805, but a TIP122 transistor and a zener. Very weird design that I have also seen in couple of other ultra cheap Chinese stuff.

Positive side: it is really cheap - under 80 €. It works - I bough it some years ago and still no problems. All the tips and replacement parts are available really cheap also. So, I recommend it.

Front side of the board. Notice LED driver mounted on an angle.

Front side of the board. Notice LED driver mounted on an angle.

The upgrade: It actually had a lot of Y2 capacitors from power lines to mains earth. But I live in an old soviet building where is no mains earth. So I added more capacitors. Mains line got a biggest X2 that I found. Circuit 5V power line got couple of big electrolytes and some of small ceramic capacitors.

I also found the soldering iron tip grounding line and added 1 MΩ resistor between it and the ground. This gave me the ability to solder live circuits. Before I had couple of nasty incidents.

Posted in Teardowns and reviews | Comments (0)

Schmitt trigger oscillator

jaanuar 23rd, 2014
by jaanus

So I wanted to study RF. To start with the most basic I wanted to build an oscillator. All the places were full of fancy and hard schematics. But to understand the need for good we must try the worst. The simplest and worst oscillator seems to be Schmitt trigger one. Information on in is scarce, but there is some information about it in AN-118.

The idea of circuit is that inverter with schmitt trigger input feeds into its own input through RC circuit. Frequency is dependant on selected R and C values.

I used 74HCT1G14 inverter 1 nF capacitor and 100k 25 turn trimmer. All the signals looked fine on the oscilloscope, so I started to increase the frequency to see how far can it go. Datasheet says that rise time is about 5 ns. That should get up to 100 MHz output. However I'm only able to get about 75 MHz out. The more frequency goes over 10 MHz the more the output looks like sine wave and the less like square.

But we still don't have answer why is it so bad. Signal looks okay on the oscilloscope. Time to get out "spectrum analyser". It is a DVB-T dongle with GNU radio software from computer side. Quick look on the waterfall display shows how awful the signal is. To give perspective - the whole frequency band I was targeting is 50 - 52 MHz.

Spectral response of Schmitt trigger oscillator

Spectral response of Schmitt trigger oscillator

The part on the top where the signal is weird is part where I switched off the power.

Posted in RF | Comments (1)

ESTCube-1 works!

mai 8th, 2013
by jaanus

 

ESTCube-1 satellite piezoelectric motor driver

ESTCube-1 satellite piezoelectric motor driver

ESTCube-1., the cubesat satellite project I have been a part of over a year was successfully launched couple of days ago. It was on Vega rocket start on 2013-05-07. CW morse beacon is broadcasted on radio amateur frequency 437.505 MHz.

I was mainly in the hardware team designing and manufacturing the final circuit boards using components tested by people before me. Most of my time was spent in working on electrical power system, but I also helped with attitude determination and control system board layout. Most independent work I spent on one of the payload circuit boards. I designed and assembled piezoelectric motor driver boards as my thesis work.

Long live the satellite! I will work on many more satellites.

Posted in Space | Comments (0)

Owon DS7102V teardown and review

aprill 23rd, 2013
by jaanus

Some time ago I bought myself a Owon DS7102V 100MHz oscilloscope. It is similar to the Rigol entry level scope DS1102E, but thinner and with bigger screen. Oh, this beautiful screen, totally worth the money. But as time passed first flaw of this eBay originated scope surfaced - the fan broke. It didn't stop, it just started to make screeching noise whenever I turned it on. When taking aparart for the first time I also managed to break soft power button.. Oh well. I ordered new 12 V 60 x 60 x 10 mm fan and KDC-A11 power button to fix it.

Internal layout is really impressive. One third of the scope is cheap power supply, middle section is battery compartment, and all the scope electronics is one small PCB. Whole scope worth of electronics small enough to put in pocket.

Interesting chips I found from scope:

Internal layout of DS7102V

Internal layout of DS7102V

DS7102V power supply

DS7102V power supply

Old KDC-A11 next to new one. Slight problem with pin sizes.

Old KDC-A11 next to new one. Slight problem with pin sizes.

LCD connector board

LCD connector board

Small bodge inductor, probably against ripple on the line.

Small bodge inductor, probably against ripple on the line.

Keyboard PCB

Keyboard PCB

Analog board top view

Analog board top view

Top view with cheap looking ADC, FPGA  and ports.

Top view with cheap looking ADC, FPGA and ports.

Filters and amplifiers

Filters and amplifiers

Signal relays and more analog stuff

Signal relays and more analog stuff

Posted in Teardowns and reviews | Comments (1)

Free sensitive thermal vision

märts 28th, 2013
by jaanus
Powered up board drying from acetone.

Powered up board drying from acetone.

My circuit board with MSP430FR normally took ~ 3 mA from 3.3 V line. But one evening, it started taking 200 mA. It seemed to function correctly but the power had to go to somewhere. 200 mA * 3.3 V = 660 mW. It is not enough power to burn the fingers so how can to track it down - use drying solvent. Normally I clean my boards with acetone (but isopropanol is better) so I just wiped that to random components until I noticed that the die part of the MCU was drying much faster than other bits of the board. After replacing the MCU the current consumption dropped back to 3 mA. The resistivity of acetone is in the order or megaohms so no problem with misoperation.

Posted in Small projects | Comments (1)