Category Archives: In English

The schematic for digi interface (ham radio)

Here is the schematic for my old digi interface. It is very basic interface with two RX lines. I made the printed circuit board years ago but was never drawn the schematic for it. Some people had asked it so there it is. It may not match perfectly with the board layout but the idea is the same.

I am going to design a new version with some improvements later. All suggestions for the new version are welcome. I will share the circuit and the board layout so you can build it too.

As you can see there is nothing new in this circuit. The same circuit has been published many times before. My whole point was to make the nice board for it. I added two RX lines for radios like FT-1000MP etc.

CQ World Wide 160m CW Contest

I participated in the CQ World Wide 160m CW contest last weekend. There were many stations around the world on the air. Even with my poor antenna and low power I made 260 QSO’s. I did not take the competition too seriously and worked just about little less than 13 hours. So my off time was over 35 hours. At the first night I was supposed to work more but did fall a sleep soon when the contest started.

I worked 35 different DXCC’s and heard couple more but was not able to work them. I am happy with the results. It is not easy to get a QSO outside of Finland on the 160m band without heavy antennas. And of course the most important thing in contesting is to have fun.

Many thanks for everyone for QSO’s. It would be nice to get your QSL cards via bureau. SWL cards are also welcome.

73 de Reijo OH7GGX




I have made some changes to my website. Some of them are happening just “behind the scenes”. I have moved some articles and pages from the old site to the new one. So if there are broken links or missing pictures please forgive me. Of course it would be nice to let me know so I can fix them. I am going through them as I have time.

There is also coming new articles and pages. Some new electronics projects too. Take a look what’s here at the moment and please come back to see something new later. I might put some titles what’s coming for example.

73 de Reijo OH7GGX

Component name abbreviations

Have you ever wondered which abbreviations to use when labeling components? Even when using just one design software, there might be different abbreviations in different libraries. For example, a crystal from one library can be labeled as Q1, then you add a transistor from another library and it will be labeled as Q2. Nothing sense. Sometimes when adding IC’s from different libraries, one is labeled as IC and another one as U. They should be both labeled as IC or U. I have seen crystals labeled as Q, X, XTAL, Y, etc. Which one is right? Or with transistors in different schematics it can be Q, T, TR, etc. Connectors might be X, J, P, CON or almost anything. There are some standards, but different kind of abbreviations are still widely used.

To clarify my own designs, I have decided to use following abbreviations. Earlier designs might use different abbreviations, but for every new design I will try use these as much as possible. This list will be a note to myself, but feel free to use it also if you want. They are not all standard, so you might want to check some abbreviations which one to use.

AE – Antenna
AT – Attenuator
BR – Diode bridge
BT – Battery
C – Capacitor
D – Diode (also Zener diodes)
DS – Display
F – Fuse
FB – Ferrite bead
FL – Filter
J – Connector (jack)
JP – Jumper
K – Relay
L – Inductor
LCD – Liquid crystal display
LDR – Light denendent resistor
LED – Light emmitting diode
LS – Loudspeaker
M – Motor
MIC – Microphone
(P – Plug connector)
PS – Power Supply
Q – Transistors, FET’s
R – Resistor
RN – Resistor network
RT – Thermistor
RV – Varistor
SW – Switch
SCR – Silicon controlled rectifier
T – Transformer
TC – Thermocouple
TP – Test point
TUN – Tuner
TVS – Transient voltage supressor, ESD-guard
U – Integrated circuits, operational amplifiers, optocouplers
V – Valve tube
VC – Variable capacitor
VR – Variable resistor
Y – Crystal / Oscillator

If you disagree with some abbreviations, feel free to comment.

Simple board for GPS-module

This board can be used with the UTC-clock shown on previous post or with other GPS-applications like frequency standards and APRS-trackers. The board is using Fastrax GPS-modules. Other components are just for 3,3V regulation and buffering the signals in and out. There is also a place for a memory capacitor. For a long-time backup, a battery should be used.  A baudrate can be selected with jumpers on the board.

Here is the board layout from Eagle:

Some ready boards for my applications:

UTC-clock with GPS-synchronization

I wanted a clock which is always on correct time. Of course that should be in UTC-time, because I’m going to use it with my ham radio hobby. The clock is using a AVR-microcontroller and a RTC-chip. Synchronization is made from a GPS and time (and date) is shown on LCD-display. There is also a connection for a computer, that can be used to synchronize the computer.

The data from the GPS is read trough RS232/TTL-converter. The microcontroller will parse the data and update the RTC-chip. The RTC-chip is running independently with it’s own clock-crystal. There is also a battery backup for RTC, so time continues running while the other circuit is powered down. The connection for a computer can be configured in two ways. The data can be read straight from the GPS, or from the microcontroller. This can be selected with jumpers on the board. There is also two EEPROM-chips on the board for future applications. LCD-connection is standard HD44780-connection. Depending on a size of the LCD, there can be shown also other information from GPS, like a latitude and longitude. I have also a option for a digital temperature sensor. Some other connections has been included also for the future applications, so I don’t need a new board when I want to add something.

Here is the circuit:

The final board (without the lcd and an enclosure):


CAT interface

I’m using opto-isolated interfaces for connecting my radios to the computer. Here is the CAT-interface I have made. It can be used with different kind of radios. Part list will vary, depending of radio used. I’m using it with Yaesu FT-1000MP. Example IC1 have to be selected depending of which signal levels your radio will use. FT-1000MP uses RS232-levels, so 74HC04 should be fine. With TTL-levels you should use 74HC07 or 74HC17. For Icom, there is a jumper for connecting RXD and TXD signals together. Some other components have to be changed also. I haven’t tested this with Icom yet, so I’m not sure is it working or not.

Here is the schematic:


Here is the board:


Part list for Yaesu FT-1000MP:
X1 – X2 = D9-female connecotr
X3 = RCA-jack
JP1 = Do not assembly this for FT1000MP
R1 = Do not assembly this for FT1000MP
R2-R4 = 475R
R5-R6 = 4,7k
R7 = 10k
R8 = 0R = Jumper
R9 = Do not assembly this for FT1000MP
C1, C3 = 100nF
C2 = 10uF 35V
C4 – C7 = 10uF 35V
C8 – C9 = 10nF
C10 – C11 = Optional filter capacitors. I don’t use them, but you can try. It can help or make things worse.
C12 – C14 = 10nF
D1 = 1N4148
D2 = 1N4004
T1 = BC547
OK1 – OK2 = 4N25 or equivalent
IC1 = 74HC04
IC2 = MAX232 or equivalent
IC3 = 7805

Computer side of interface is powered from RS232-port. You have to set RTS and DTR lines high from your logging software. Radio side is powered with RCA-connector. You can take the power from radio or external power supply. Ensure that your radio can supply the current needed. Otherwise it is safer to use external power supply.

Some possible improvements for new versions:

  • Capacitors could be with 5mm grid, which seems to be more common and easier to get, at least here in Finland.
  • Voltage regulator could be replaced with low-drop type.
  • Some pads could be larger.

Here are some pictures of my interface:

CAT interface board.

CAT interface with IC-holders and connectors assembled.

All components for FT-1000MP assembled. Some components should not have been assembled for FT-1000MP.

CAT interface assembled to an enclosure.

Ready interface.

5V regulation board using LM2575N-5.0

Here is a simple voltage regulation board for LM2575N-5.0 regulator. Depending on components used, it can supply maximum 1A current. LM2575 is a step-down switching type regulator. I made some tests between LM2575 and MC34063, and it seems that LM2575 was the better one in my case. Or at least it was easier to make it work reliably.

There is two versions. Both circuits are from datasheet. One with only one inductor and second one with additional filter. In many cases the simpler one is just fine. I made the second one for use with equipment that needs clean voltage. It’s not bad even without additional filter. For comparison, with MC34063 it seems to be needed much more filtering. These were not professional tests, so someone might get different results.

If you need a really clean voltage, then you should use linear regulator. Switching regulator is not always a best choice, but it will have good efficiency. With filtering, it can be used on many cases.

You need to ensure the current rating of inductors. Capacitors should have low ESR.

Here is the simpler circuit and board for it:

LM2575 circuit without additional filter.

LM2575 board without additional filter.


Here is the circuit with additional filter:

Circuit with additional filter.

Board with additional filter.

Eagle: Text tool and Gerber files

I had a problem with text tool in Eagle. Text was normal in Eagle, but when exported it was bigger than it should. That’s not good when you are sending Gerber files for manufacturing.

Here is an example:

Text seems to be normal in Eagle.

This happens when exported. Text is overlapping with another.










Problem was that I was using proportional font-setting instead of vector. When exporting Gerber files, there is no support for proportional font and that’s why it happens. So, always use vector setting when you are going to export your design.

To solve problem, select “info” tool and click your text.

There is “Font” selection. Change “proportional” to “vector”.

Now, text should be seen as it will be exported.

To avoid this in future, you can change your user interface settings. On Eagle’s main display, select Options -> User interface.

This kind of window should open:

Check option “Always vector font”.

That’s it.

Lead-Acid battery charger

This is a simple lead-acid battery charger build for my own needs. Lead-acid batteries needs to be charged first at constant current and then at constant voltage. There are also some integrated circuits made for lead-acid batteries, but this simple circuit works fine for my purposes. It is built around L200 regulator. I tried LM317 also, but wasn’t pleased with it.

Circuit is mostly from L200 datasheet. It can be used with load connected to battery if load is smaller than charging current. Of course current is then shared with load and charging takes longer. Charging current can be set with R2. R3 is for voltage adjust with R1. D1 is to prevent battery discharging trough charger if charger will be switched off and battery still connected. Remember to use a heatsink with L200.

Circuit is simple:

L200 Lead-Acid battery charger

Here is board I designed:

L200 charger print

This board can be used as normal voltage regulator board also. Current sense resistor can be replaced with jump wire if you don’t want current limit. You can also drive some 2N3055 or similar transistors to get more current.

First tests. It’s working great!