_ THIS SECTION HAS BEEN SUPERCEDED BY THE INFO AT TOP OF THIS PAGE.

UPDATE May 21st 2025

A new version of my BLUETOOTH switching board. (Now V2)

BLUETOOTH switching board is currently being worked on, which supercedes the one below. This one should be simpler and cheaper to build as it uses IC's to do what multiple transistors did in the version below. It also uses a larger (and cheaper) 2.8" ILI9341 TFT screen rather than the ESP32 version with integrated TFT display. The ESP32 Development Module is much cheaper also. It also provides outputs for the VHF and UHF bands. The extra screen space will allow for larger text etc and other information if required.

I am currently waiting for the draft PCB to arrive, to build and test it. Due in June.

Briefly, it uses 2 x MCP8574 devices plus 2 x ULN2803 parts in place of the smd transistors. There are 10 band (V1 was 6 bands) outputs, PTT out and two spares which can be programmed with other CIV commands.

NEW May 26th 2022 BLUETOOTH SWITCHING (V1 is current, will be replaced by V2 above when tested.)

Apart from the above methods for band switching and PTT buffer, a new project was to investigate using Bluetooth (BT) in the IC-705 to an external Micro using BT to do the switching. This is much nicer/neater, as no wiring is required to the IC-705. The idea is to use Blue tooth to switch and external Amplifier and Low Pass Filter. (Info on that project later.)

I take no credit for this software as the majority (99.99% !) was done by Wilfried (DK8RW). I acted as a 'tester' for the project with some minor sketch changes to suit this application. It uses an ESP32 "TTGO" board which is available from the usual on-line sources. This board has an in-built 240x135 pixel colour display which is used to display the current Band and Frequency plus Rx/Tx status. Some output buffering is needed as the ESP32 runs from 3v3.

Wilfried has a Github account here where the source code will be uploaded. See the Examples sub-directory.

Details of the Schematic for my build is below.. It includes buffers for the external LPF and PTT switching.

This is the TTGO board: It should be possible to use any ESP32 board with no display, and add an external display, although I haven't tried it.

Showing the interface in Receive and Transmit modes. (Actual TFT quality is much nice than the pictures here.)

Out of band is shown as:

Early version Build information: Now superceded!

Schematic includes details of buffers used to interface to IC-705 and in my case, a PA which requires a '+ve bias' supply to transmit.

It may look a little convoluted but the output of the 74HC42 switches from a high of 3.3v to a logic low level. This requires another inversion to produce a low going signal, suitable to operate the LPF and change over relays which are supplied with 12v.

I use the G6ALU PA and G4TZR Low Pass Filter, so the Sch is designed for that.. Both are detailed on Steve's G6ALU web page. SEE LEFT SIDE OF PAGE.

The Schematic caters for the full "HF" 10 bands from the IC-705, (160M to 6M) but in my case I only built a 3 band LPF for 80, 40, 20M bands. A low going output is also provided to allow use of relays to switch in the Linear/LPF relays when in transmit mode. My 3 band version of the G4TZR LPF is here.

Overlay by Ref number and overlay by values (ie what's on the PCB)

Bill of Material (BOM)

I designed a PCB for this project, which will cater for 6 bands. It should fit onto an ~63 x 63mm PCB which will contain the ESP32 TTGO board and allow it to be fitted to the front panel of the Amp for indication of state, as above.

Many LPF designs allow TWO Bands to be combined into one filter, eg 30/20M, 17/15M & 12/10M bands. This can be catered for, by allocating two bands to the one output, in the 'constexpr uint_t band2BCD' section, Line 145, in the "z_userprog.ino" file. I will give further details of this later.

NOTE: The PCB uses mostly smd components. If you follow my design, don't be frightened of smd, only simple tools are needed. Ones you probably already have,

• soldering iron, small tip
• side-cutters,
• tweezers,
• magnifying lamp or headset
• and solder of course. (PLUS Flux either as a liquid or in a flux-pen is also useful)

Software: https://github.com/WillyIobrok/CIV_template NOTE: must use the "z_userprog.ino" file contained in /Examples/VK3PE directory for the example on this Github page.

I measured the PTT delay: from PTT out of the IC-705 to PTT out of the interface, at a max. of 24mS. There are three settings in the IC-705 menu available to delay RF output. Set it to 30mS.

NEW VERSION Draft Sept 2025 I am currently working on a newer version of this board that also outputs discrete voltage steps for band changing, as used in the Xiegu XPA-125 linear amp. I don't actually have this amp but a ham contacted me recently to add this facility to my existing code, linked above.

I'm not quite ready to release the new version as I have a new PCB coming that incorporates a buffer for this mode also. This version will still have the separate outputs to drive a 'discrete' LPF design.

UPDATE Feb 17th 2026

Chris, DK8HC, has built a version just for interfacing to the XPA-125 linear amp. It gives a DC voltage output for XPA-125b band switching , plus a PTT output. Google his Github page for details. Power is from USB-C power delivery and a LM7805 linear regulator, or similar.

The TTGO module is not shown, but plugs into the 2 rows of sockets on the PCB.

The ESP32 module plugs into this PCB.

UPDATE Jan 27th 2023

Lucien sent a picture of his version of the BT Interface. He modified the sketch (code) a little, to suit his application, see below. He added VHF and UHF for switching.

Jan 2023

Hello Glenn,

Here a message from the Netherlands.
I few years ago you send me a few PCB's for the atu-100, maybe you remember it.

But now I want to show you what we made and adapted from the design on your web site. It is a variant of the design of the IC-705 BT controller.
We have adapted the software to my wishes and that is an extension of contacts for:

TX only HF, TX only VHF, TX only UHF (to control extra amplifiers),Coax relay HF-VHF-UHF (No Duplex filter needed) , an analogue output for band data control to a Xiegu XPA125b Amplifier. and added 60 meter band.

I'm not a good Kicad PCB designer and I made them the old fashioned way, but it works perfectly.
On my https://www.qrz.com/db/pe1ofo page you can find the data of the project. (scroll down a bit)

I hope you like it and you can of course share and or copy everything!

Best regards from the Netherlands!

'73 Lucien PE1OFO

I also have a design similar to the above, for Atenna Switching, see this Link.. <vk3pe>

Many thanks to DK8RW for the code & PU5VEN for assisting with PTT function.

External linear amp. PTT buffer.

There has been a lot of discussion on the groups.io 'IC-705' group about interfacing to the PTT output of the IC-705, for connecting to various brands of Auto Tuners. There have been several cases of users having to return their IC-705 for repairs, after the PTT port transistor/s have died.

It's not helped by the fact that currently, ICOM have not released a Technical manual for the rig, so not much is known about the IC-705 ports.

Ron, VK3AFW, has designed an 'interface' schematic to avoid any potential conflicts with external equipment and the IC-705.

Since I plan to eventually add a 50-100W linear to my rig on occasion, I have followed Ron's suggestion. I added an optional relay output also.

Version 1.0 PCB:-- (no PCBs available now)

This is Ron's Schematic for his buffer (plus my added relay). (pdf File updated 25th Jan 2022) and the draft PCB layout.

****As presented above, if the IC-705 is not connected, the V1 PCB will output a logic low 'PTT' signal to whatever is connected. Usually not a problem but I plan to add a couple of parts in the bread boarding section (lots of holes in top left area) to avoid this. The 'V2' PCB will have provision for these parts. (not yet tested)

5th April, 2021 The V1 PTT Interface PCB arrived. The optional relay for a 'normally open contact' PTT out, is not fitted in the pictures. The PCB is ~41 x 26mm.

20th April 2021: A 'gremlin' (brain fade) got into this V1 PCB and the 3.5mm input connector has the 'TIP' & 'RING' reversed. Easily fixed by a single track cut and addition of a short wire on the bottom. However, I have updated the PCB to V2.0 as below . V1 mod Details are here.

21st April, 2021: V2.0 Bill of Material (BOM) pdf & Xcel (right click to save) is for a V2 pcb but notes on the BOM and V2 Sch, will show what's required for V1.

Version 2.0 PTT buffer PCB:--

A component overlay drawing for V2 is here. If you wish to experiment on V1, you can add the three parts using the unused proto holes section in top left corner of the PCB. NOTE: check data sheet for the 2N7000 as it's possible there may be devices with pin-out reversed. So far though, mine have been as expected and shown below.

I have a few spare V2 PCB's. Gerber's will follow later.

Assembly: I don't give any part by part assembly details, It's assumed you have some basic knowledge. But with smd parts, best to fit the low height parts first and work up to the larger (higher) parts. See the links above for Schematic and BOM.

Sept 28th 2021:- F1FCO has built one of my early V1.0 PCB's and reports "everything worked perfectly". Pierre didn't have the 2N7000 so used a BS170's instead. (note different pin out)

Brian, AB6UI, also built the interface but using the "V2.0" PCB and reports it works well.. Brian is not using the Jack, as the PCB is being incorporated into some equipment. And note the superb soldering by Brian!

NOTE:- Q1 is fitted as shown, NOT as the overlay.

Craig, N6CAV, kindly provided a 'corrected' overlay overlay drawing, showing the FET's and corrected text on right side,see below.

Dave, G4FRE, has also built this PCB from my Gerber files.

I may have some of these V2.0 PCB's available. Gerber files for V2.2 are provided below if you want to order them.

Nov 2021: I built another V2 board below with new 2N7000's bought from a local source and assumed to be 'real'. Preferably from a known good source although I don't know if this is a general problem. I checked data sheets for several brands and the 2N7000's were orientated as mine is below.(the overlay for one device is reversed)

I don't really plan to 'fix' the PCB overlay as it's not a deal breaker, as long as you are aware of it.

TEXT ERROR:- (but see paragraph below also) As it happens, the overlay text on the output connector is also incorrect! (I must have been half asleep that day.) The pin marked 'FET' is actually the normally open relay contact. The pin marked "PTT" is the FET output if the relay is not used. Both are active LOW.

GERBER FILES:-

Aug 19th 2023:- The TEXT ERROR and FET orientation has been corrected, see below.

The new V2.2 Gerber files provided on an 'as-is' basis. You will get 6 PCB's on each panel ordered so if you order the minimum 5 panels (100x100mm) you will actually receive 6 * 5 = 30 PTT Interface boards. All care taken but it's up to you to check the files with a Gerber viewer. Share with friends or anything you wish. BOM is unchanged. Send me an email if you make the PCB from my Gerber files, on how you went.

I used 5v6 Zener diode (D3) as that's all I had in stock, but it's probably better to use a 4V7 400mW type. The Zener plus R5 & R6, keep the interface 'PTT out' inactive if the IC-705 is not plugged in. Otherwise you will have an active PTT output to your amplifier, when the IC-705 is not connected, which may or may not be an issue to you. Adding these parts is thus entirely OPTIONAL. Beware, if the Zener goes open circuit for example (highly unlikely) , then 12v will appear on the IC-705 PTT output. Albeit via over 10k ohms in series. It might damage the IC-705. Or it might not. Most likely not, but I take NO responsibility for this..

See notes above and note Q1 orientation..

Version V2.2 overlay, by component values. See actual PCB for component ref. numbers.

Interfacing the ATU-100 to the IC-705 with an ATtiny85 micro.

NEW Feb. 4th, 2021 Interface to N7DDC's ATU-100 auto antenna tuner.

Most of the "interfaces" I have seen or heard of, simply use the ATU's "TUNE" button to initiate tuning with the ATU-100. ICOM provide a "TUNER" button on the IC-705 itself which seems to me the more elegant way to do it.

The ATU-100 is available from a number of sources, from a kit to a fully built tuner in a case. Kits start about US$30 which is what I bought. Some kits don't have the smd parts pre-soldered, look for one that does if you don't like smd or just want to save time!

It actually turns out to be a little difficult to do, until one comes to understand the workings of the IC-705 "TUNER" function. Information on this is scant. I won't go into the details here for now, the Sketch will give you the details.

I decided to use an ATtiny85™ using the Arduino™ IDE to develop code for the function. Due to the lack of a meaningful way to monitor things while testing, I moved over to a Arduino NANO which allowed me to use Serial.print statements in the sketch to help debugging the sketch.

The result is that either the ATtiny or NANO could be used, as I have made the sketch able to compile for either device. The ATtiny85 requires a programming adapter to be made to program it, which is a nuisance if you don't have one already. Information for this is widely available on the Web. I used an Arduino UNO board with a home made adapter on top. See picture below. You could also use one of the 'prototype' boards that fit the UNO board for a nicer look.

Operation is simple, select the IC-705's Function...'2'... and the TUNER button should be not be grayed out when the interface is connected.

A short press of the button will RESET the ATU-100 if required. (All relays off etc)

A longer press will show the button as "ON" and the IC-705 will transmit and the ATU-100 will tune. There is a time out timer in the sketch to limit the tuner time if a match is not found. (The IC-705 also has a built-in timer of 60 seconds if no tune is found)

My programming adapter: pictured. I see that amongst others, SparkFun® Electronics have a ready made programmer available. (See Digikey.com "PGM-11801". Also the SparkFun web pages. I have not tried this programmer, but have no reason to believe it wouldn't work. I used what I had available.

Setting up the ATU-100 for low power tuning.

Ideally, the ATU-100 needs some changes to allow lower power use with the IC-705. I altered the turns on the SWR transformer from 10 to 6 and also set mine up to tune with 1 Watt rather than the default value of 5 Watts. Location 05 in the EEMEM needs to be changed from 05 (5W) to 01 (1W). This requires the use of a PIC programmer to re-program that location. I used a PicKit3 to do the job. Clones of the PicKit3 are readily available on ebay etc. There are YouTube videos on how to do this, available.

June 2021: Brian, AB6UI reports this method works well. How to Program an Attiny85 From an Arduino Uno : 7 Steps - Instructables

UPDATED June 2024 :

Schematic of my dual interface version is HERE. (The schematic shows both the ATtiny85 and a NANO, only one is actually fitted.)

Bill of material HERE. <Right click to save text file>

In the sketch, there is a directive to use either the NANO or ATtiny85 at about line 44. Make selection then compile in the Arduino IDE.

Line 44 changes.

Please email for the sketch. (vk3pe see QRZ.COM for email address)

ATtiny85 only version, below. This is the final version of the ATU-100 to IC-705 interface.

The ATtiny based PCB is smaller and now assembled also.The LED indicates 'tuning' is taking place.

V1 PCB is about 38 x 31mm. See also V2.0T version below.

NOTE: V1.0 board, The LM317L should be fitted as per the PCB above, NOT the overlay ! (V2.0T is OK)

Sept 2021, V2.0 PCB. Somehow the PCB in the 'R1' area is missing the pads. BUT see below for corrections. See the picture below, the left bottom PCB in a panel has R1 with pads but the PCB to the right, has no pads. Weird.

To correct this, scrape the solder resist off the tracks in the R1 area and fit a short across the pads, then mount R1 onto the pads/holes just above. Ignore R10 as it's not used. ** Click on the pictures for larger size. ** (Ignore the circle around R2)

My PCB was designed to fit behind a panel, so the stereo socket is easy to use, plus the LED can project through a hole to show the status also.

Both PCB's require a 12v connection, as for some reason, ICOM didn't make available a switched 12v output. Not normally a problem as the ATU-100 or other device will require 12v anyway.

However, the ATtiny only version Schematic is available here.

Parts overlay,for above PCB, (updated 3rd May 2021) NOTE LM317L orientation fitting! Bill of Material (BOM) here. BOM is only for the actual PCB, you will need for example, a 4 pin socket header for the cable to the ATU-100. Wire, Mounting hardware etc.

UPDATE Aug 2023 The above PCB fault (missing pads) has been corrected on 7th Aug 2023. Schematic is identical to above link. The layout has changed a little and it's slightly larger also, so here is the new overlay by value. below. NOTE, C2 only (100nF), does not have dual footprints. ie it is an SMD part and does not have holes also for a through hole part. In actual fact, it could probably be deleted.

Gerber files See below. The Gerber file actually contains 4 PCB's that are V-grooved so each PCB can be 'snapped' off. ie If you order the min. 5 panels from typical Chinese PCB suppliers, you will get 16 actual interface PCB's. Share with friends etc.

 

ATtiny sketch:- see further down !! October 2024

 

Overlay by component values.

PCB's like the V2.0T immediately above, or the 'V2' ,might be available, ask. (see QRZ.COM for vk3pe)

October 2024:- The current Version is now V2.1T, virtually same as pic above. Here are the Gerber files. NOTE: I have not had this pcb made myself so Gerbers are as-is !

October 2024:- The Software is Here. This software also covers the NANO version if one wants to build a version using it.

Connection to the IC-705 & ATU100 requires a stereo 3.5mm plug to plug cable. These can be purchased on-line or it's simple to make one, preferably using twin core shielded cable. A cable needs to be made to connect the ATtiny PCB to the ATU-100. Since I assume that the ATtiny PCB will be housed inside the ATU-100, then just a short cable needs to be made. The 'A7' connection on the ATU-100 is a small pad on the bottom of the ATU-100 PCB. Ignore the 'A6' pad. A drawing might be uploaded, as soon as I can draw it up although should be fairly clear from notes on J1 of the Schematic or the overlay link above...

NEW Apr 27th, 2021: James, W0FIP, contacted me with a suggested modification to the sketch, which I have incorporated into the code. James reported the interface works very well. James also tested it on other ICOM rigs. James didn't use a PCB, in true Ham spirit, made his own version using some proto type material. Great work.

Updated 11th May 2021: The V2 version can take either smd or through hole parts, see pics below. Same layout and size though as V1. The LM317 orientation on V2 is corrected.

I may have a few spare V2 boards available. While "BC548" transistors are specified, most any NPN transistor should be fine. BUT, please check pin outs before fitting !

SOFTWARE

Sketch will be on request at the moment and subject to a disclaimer that it may not work for you.. Of course this involves connections to your IC-705 and I can take no responsibility for any damage that may occur if you do this incorrectly.

15th Feb.., 2021:- My sketch is working on both the Arduino NANO and the ATtiny85 versions. I did discover though that pin 'D5' on the ATtiny can't be used as a true I/O pin so moved some pin functions.

There are very few parts on either board, as you will see on the Schematic. ATtiny Link above.

How it works:

When the interface is connected to the IC-705 via the 'TUNER' 3.5mm socket, it enables the TUNER button on the screen in Function...2

The TUNER button now becomes active and is no longer 'grayed' out. If you now 'long' press the TUNER button, a blue line will be visible around the button and the interface will become active and command the ATU-100 to auto tune. At the same time, the KEY line to the IC-705 is set low, telling the IC-705 to transmit a carrier. In the ATU-100, the A7 line will go HIGH signifying it's in TUNE mode.

Once the ATU has finished tuning, the A7 line underneath the ATU-100 PCB drops from a high level to a LOW level, and the interface pulls the KEY line high again and the IC-705 stops transmitting.

If you make a 'short' press of the TUNER button, the ATU-100 will be RESET.

**While TUNER is active, pressing the PTT button will also cause the IC-705 to transmit a carrier and make ATU tune. If it had already done a tune then the ATU-100 does nothing as it retains the tune itself.

It's a bit inconvenient to activate the TUNER button using the 'Function 2' in the Menu structure so you can re-program the VOX button to directly turn on the TUNER function. To do this, press Menu/Set/Function..scroll to screen 9/10 (shown in top right corner) and press 'Front Key Customize'. Press [VOX/BK/IN] and select TUNER.

If you use VOX normally, then you can re-program some other key (button) to do 'TUNER' function. Refer to the manual for options..

I decided to make a stand for mine to make it easier to use on the bench. It's just a simple bent piece of aluminium, with some rubber feet stuck on the bottom.

Click the drawing for a larger view. The dimensions for the hole locations are in the Basic Manual for the IC-705, page 2-2.

It's easy to modify this idea to suit your own requirements. eg add a socket for a vertical whip antenna.

There's a commercial antenna add-on mount here. Check Amazon.com for details.

PERSONALLY, I WOULD JUST MAKE MY OWN WITH SOME SUITABLY BENT UP ALUMINIUM SHEET.

Update 6th October 2021: N7DDC has released a QRP version of his ATU, the "ATU-10".

It has the IC-705 interface built in. You might like to consider that option. N7DDC has Gerber's available for the PCB but note some parts are very difficult to get right now. I have re-designed N7DDC's PCB to use some much easier to find (larger) parts. And much easier to solder also. See link below.

A link to my version of the ATU-10 using much easier to find (and solder) IC's used on the board. It slides into a 100x71mm extruded case available on eBay.

My version of the N7DDC "ATU-10" QRP ATU.

Below is now obsoleted by BlueTooth versions:-

1st Dec, 2020 External Band Switching

This method is superceded by the Blue Tooth versions above !

Once I finalise my external amp and LPF, I need something to switch them, rather than change bands manually on the LPF. I contacted WB9IXS, who has made an auto band change Schematic using a PIC™ Microcomputer. I contacted Jim and he was kind enough to pass on his source code. I had though some PIC16F876 devices on hand, not the PIC16F886 devices he used. A friend (thanks Ric) assisted me to alter the PIC code to use my available PIC. It includes capability actually, to compile for either PIC type. (Jim has since added a frequency readout to his code but I don't have that code)

As presented here, it will decode for these Amateur bands: 160, 80, 40, 20, 17/15 & 12/10M bands. It should also be possible to decode other bands.

The original Schematic is here.

I bread boarded the original Schematic and programmed the PIC and it works....

This is my test set-up. The LED's indicate which band has been detected. Showing 40M at present. These outputs will be buffered and fed to the LPF which in my case, requires a logic Low to change the LPF relays. The piece of PCB material is the RF input buffer stages.

There is an input RF buffer amplifier in the original design, but I found it to have some problems, so it was changed to use a high speed comparator chip and is in the actual PCB below.

Below is my actual PCB, now with a new input buffer/amp stage. April 11th, 2021

The PCB is about 77 x 50mm

RF enters the PCB at the bottom left of the PCB and is fed to the tiny comparator chip just above and to left of the crystal. The PIC Micro processes the squared up signal and outputs a Logic 'high' to the ULN2003 buffer on the right. 8 HF Amateur Bands can be detected with each band giving a LOW output to the header pin connector. In addition, if required the PCB can be fitted with 8 (0603 sized smd) LED's, not fitted, to indicate the band being decoded.

160M, 80M, 40M, 20M, 17/15M, 12/10M

At the top of the PCB is an ISP connector for programming the PIC micro device. At the bottom of the PCB is another connector which can be used to provide a serial output if needed. While not coded as such, this output could possibly be used to switch an external Linear/LPF which uses serial input.

The project will detect a signal about -20dBm typically, and up to 10dB better, on the lower bands.

NEW May 3rd 2021:- Sch here Sheet 1 & Sheet 2

BILL OF MATERIAL (BOM) (Right click to download in Excel format)

PARTS OVERLAY by Component Value NEW Oct 10th 2021 for the V3.1 PCB, but same for V3.0

Gerber files, not yet. I do though have a few spare PCB's available.

to be continued.

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