Adding a 2.8″ v6 type TFT display to your v3 – v5 uBITx

It is not difficult to add a 2.8″ TFT display to your existing µBITx.  Make sure you order a 2.8″ ILI9341 touch panel display.  These are readily available on eBay and AliExpress for under US$10, which is half the cost or less than a Nextion display.  This display, however, has its downsides … more on that later.

Wiring changes required

Ashhar Farhan VU2ESE has clarified that on the new V6 mainboard, the connector to the Raduino has two extra pins. These don’t disturb the original configuration of the original connector, they bring the Keyer pin and the PTT from the Raduino to the main board to be routed to the keyer and the mic connectors. You could still plug in an old 16×2 LCD raduino into the new v6 main board and it will work all the same.

To run the v6 firmware on a v5 board, you will have to jumper gnd, 5v and the six data lines between the old Raduino and a TFT 2.8 inch display.   This should be reasonably self-explanatory as the same data lines are used on the standard 1602 display and the ILI5341 Display.   Use readily available short (100mm) dupont style connectors to link the display with the Raduino connector.

Pictures will be posted shortly.

It is recommended that you add a heatsink to the regulator on your Raduino board, as feeding the ILI5341 will result in additional current draw over the 1602 standard display.

Installing the new firmware  

The factory firmware can be downloaded here.

Note that if you have a v3 or v4 board, the firmware will require a modification to change the IF oscillator frequency. This is because the v5 and v6 boards use a different IF filtering frequency (12MHz).  Only one line of code will need changing.   Which line? Anybody?

Upsides and downsides of this display

The upsides of the ILI 9341 display is that it is very affordable and supported by factory uBITx firmware.

The downside of this display, however, as can be seen on the demonstration video from HF Signals, is that it is very slow in operation.   This is the result of the slow Arduino Nano processor having to communicate via serial port with the processor-less ILI9341 display.

The Nextion display mod from Ian Lee KD8CEC results in a much more responsive and attractive display, updating very quickly and being able to display S-meter readings and has other features not found on the v6.  However, it does come at a greater cost.

Reference

Sidetone mod

Ashhar Farhan VU2ESE, designer of the uBITx  recommends replacing R253 (a resistor) with a 0.1uf capacitor to get the sidetone to work properly if you are encountering issues with it (mostly on a v5 uBITx).  You can also replace the 1K resistor at R250 with a  10 K resistor to increase the sidetone volume.
Ashhar was fooling around with an upgrade to the Raduino, (more to come shortly) when he noticed that the sidetone was not working properlt. After a day’s frustration, he put a scope probe on the sidetone line and saw that as the sidetone made a square wave of 0 to +5v and back, the average voltage rose to 2.5 v.  This was directly coupled  to the LM386 audio amp’s volume control. Replacing the final resistor(R253) in the low pass filter with a 0.1uf capacitor fixes the problem.
The problem was that the sidetone would work for “dits” satisfactorily, but the sidetone for a “dash” would vanish after an initial blip. That’s because the LM386 (in the v5 uBITx) was being pushed to the rail by the 2.5v DC on the input!
Reference

Addressing issues with an SWR meter and the Nextion display

Joel KD6AGW has been working on his UBiTx V5 for a few months now and added the KD8CEC update with Nextion screen and the I2C update.  He had all the features working (CW decode etc) except the SWR meter.

Joel also built a Kits and Parts SWR bridge and hooked it up to the second Arduino.  However, the meter never operated correctly.  The home brew Stockton bridge that Ian (CEC) used apparently did not have this problem.

After hooking up an oscilloscope to the forward and reverse outputs, Joel noticed that the reverse voltage would bounce up to 4 volts or so before settling down after a few seconds.  This was while the uBITx RX input was hooked to a 50 ohm dummy load.  When the probe was hooked up, the meter on the Nextion display would go high, and then settle down to a good swr reading.   However, as soon as he removed the probe to the oscilloscope, the meter would just stay pegged at very high SWR.

He ran across a blog item here (http://www.kk5jy.net/swr-meter-v1/)  about building a digital SWR meter and noted that:

“In order to prevent stray RF from getting into the A/D circuits,  a 0.05uF ceramic disc capacitor was placed between each line and the GND pin.  Since the A/D inputs are very high-impedance, and the SWR sensor outputs were meant to drive current devices (e.g., analog meters), a 75k resistor was placed across each of the 0.05uF caps, to drain the accumulated charge when no RF was applied”.

After doing these modifications, Joel has found the SWR meter to work great.

For information, here is a sketch of the circuit modification:

Following a question about power wastage in the Stockton Bridge SWR circuit Joel checked the output with the bridge in and out.   There was no perceptible difference in power out on the oscilloscope.

Reference

Variable bandwidth crystal filter

Some time ago we featured a design from Michael N2ZDB that used a Jones filter design from TenTec to produce a variable filter passband for his BITX40.

There has been more recent interest on the IOGroups BITX20 list in variable bandwidth filters in the µBITx.

Karl-Heinz DF9RU completed a build of a µBitx transceiver and found it to be an excellent learning platform. He has been toying with a variable CW filter.

Up until now audio filters have largely been adopted by members:  either active filters with operational amplifiers or DSP filters with microcontrollers.  Karl-Heinz acknowledges that these options represent easy solutions for integration into the µBITx.

Karl-Heinz has a CW transceiver HB-1B from Youkit. This transceiver has a quartz filter of variable bandwidth.  The bandwidth can be continuously changed using varicap diodes.  The circuit diagram of the HB-1B can be found here.

Karl-Heinz was impressed by the acoustic result of the simple circuitry of his HB-1B and wondered why this alternative had not previously been used?

TenTec has patented a filter design which describes the passband curves of this filter.  A German website  also documents results on the bandwidth of these filters, which match with data from the TenTec patent.

Thierry F1HSU suggests taking a look at Tasa’s site for a tunable quartz filter  : http://yu1lm.qrpradio.com/bp%20yu1lm.htm

Ashhar Farhan VU2ESE suggests that these filter designs are merely a variation of the min -loss cohn filters. As only the coupling capacitance is varied without varying the terminating impedance, we must expect high ripple at all settings except one. What does this mean? It means that the filter will exhibit ringing and phase delays.

A better option would be a smooth Butterworth response with minimum ringing at a fixed frequency.  You can vary the BFO for shifting the audio tone. A 400 hz bandwidth will be narrow enough and yet offer a brightness that we miss in more aggressive designs.

Wes wrote a paper on this on his website www.w7zoi.net.
Ted, KX4OM reminded us of the SSB6.1 transceiver, which employs a tuneable SSB filter with tuning diodes in place of the capacitors in a min-loss configuration. The rig is a basic SA612-based design which can be found here:

Allison KB1GMX suggests looking at this design as well.  It is not new and a bit tricky but works best with lower frequency crystals.

Reference

Monitoring your microphone level

Didier F5NPV notes that many options are possible to tune your AF level. Measurement tools like an ocsilloscope can tap directly at the output of the AF Amplifier.  Alternatively a spectrum analyzer can be very useful in monitoring spectrum quality.

It is also possible to use another RX, a SDR receiver or even WebSDR online to monitor your transmission in quite an accurate manner. When you establish the correct level  of gain required to generate a signal without distortion spikes you just need to calibrate a meter with the appropriate threshold value.

The µBITx does not have an AF level input monitoring system. It is simply impossible to know if the level applied from the microphone preamp is too high or too low.

in the picture above you will notice a little switch just below the vu-meter thatI use to monitor the AGC and AF input level.

Reference

100PPR encoder – mods to KD8CEC code to make it work better

Using a 100PPR encoder with the KD8CEC firmware may cause some issues as the firmware can’t keep up with the pulse train from the encoder.

Sascha Bonnet suggests some simple code modifications make a big difference. He replaced two commands (“millis” to “micros”) in the KD8CEC’s source code and my encoder worked.   Here’s his code for you to use as a template for editing the KD8CEC arduino sketch:

  1. int enc_read(void) {
  2.   int result = 0;
  3.   byte newState;
  4.   int enc_speed = 0;
  5.   unsigned long start_at = millis();
  6.   while (millis()  start_at < 50) { // check if the previous state was stable
  7.     newState = enc_state(); // Get current state  
  8.     if (newState != enc_prev_state)
  9.       delayMicroseconds(1);
  10.     if (enc_state() != newState || newState == enc_prev_state)
  11.       continue;
  12.     //these transitions point to the encoder being rotated anti-clockwise
  13.     if ((enc_prev_state == 0 && newState == 2) ||
  14.       (enc_prev_state == 2 && newState == 3) ||
  15.       (enc_prev_state == 3 && newState == 1) ||
  16.       (enc_prev_state == 1 && newState == 0)){
  17.         result–;
  18.       }
  19.     //these transitions point o the enccoder being rotated clockwise
  20.     if ((enc_prev_state == 0 && newState == 1) ||
  21.       (enc_prev_state == 1 && newState == 3) ||
  22.       (enc_prev_state == 3 && newState == 2) ||
  23.       (enc_prev_state == 2 && newState == 0)){
  24.         result++;
  25.       }
  26.     enc_prev_state = newState; // Record state for next pulse interpretation
  27.     enc_speed++;
  28.     delayMicroseconds(1);
  29.   }
Reference

Full assembly of a uBITx

Jonathan Kayne, KM4CFT, who is studying at Virginia Tech in the USA asks on the IO Groups BITX20 list whether it is possible to do a full assembly of the uBITX.   That is, he wants to start with a bare PCB and hand solder on the SMD components. He plans to use it in a school project.

He received several replies to his query.    Jerry KE7ER suggests:

Be aware it might not be as trivial as it looks.

The transformers are described here:
http://www.hfsignals.com/index.php/ubitx-circuit-description/

Search for “Coil Details”.

The KiCad files are not available, that was some sort of requirement
when they set up HFSignals to build this stuff. Perhaps to get a business loan they had to keep some part of the design private. The remainder of the design is open source, and building from scratch is encouraged. The uBitx is a two layer board, the bottom side is mostly ground plane. Perhaps just build “ugly style” or “Manhatten style” on copper clad circuit board, that way you have a solid ground plane under the entire design, which is highly recommended.

All quartz crystals in that IF filter should be matched by hand to within 100hz or so, that means building a crystal oscillator and having some way to accurately measure frequency. If your quartz crystals have different characteristics than what hfsignals uses, you will need some way to determine the passband of the IF filter and adjust the filter shape as described in Experimental Methods in RF Design (and/or search for Dishal on the web).

You will need some way to sniff and measure RF, an Antuino would be ideal, though you might get by with a diode RF probe and a Harbor Freight DVM. A good scope would be nice, perhaps 50mhz or more of bandwidth. The nanoVNA would be worth looking into, shows complex of 1 and 2 port networks, and thus is an education in itself.

If you are serious about studying “RF and Microwave”, all of the above is worth the investment.

And lastly, maybe you could consider getting a working uBITx from HF Signals, simply so you can  know for sure what the signals levels really should be when yours doesn’t work.  Many have built radios like the uBitx from scratch, but few find it easy.

Ashhar Farhan VU2ESE, the designer of the µBITx has indicated he can arrange for a blank PCB.   He notes, however, that there is very little education in it!   To build an actual ubitx all by yourself would be a better learning experience.

Although the µBITx is a double conversion design, it is actually quite easy to build, stage-wise.  Ashhar suggests building the IF amplifiers first.  You have to build six of these. After getting one going, the rest can be duplicated.  He suggests that each is built on a separate 2″x2″ copper board.

After the IF modules have been built, you can hook up a raduino from the Si5351 board from qrp-labs and an antuino.   Using the antuino as a signal generator, you can test and align the 45 Mhz filter and the LPF.  At that point, you are done with the RF parts and you can choose to go with any audio amplification system.

Ashhar encourages experimenters to build their µBITx one stage at a time, then test, measure and move on.    He suggests it is a great education!!

Reference

Digital interface kit for your uBITx

David N8DAH is now producing a very handy digital interface kit.  This is a Gordon Gibby KX4Z design, and it features:

  • On board 5v regulator that you can power from 12-13.8v or you can leave it off for direct 5v input.
  • Built in VOX PTT via reed relay
  • PTT LED
  • Input and Output gain control
  • Audio Isolation transformers 600:600ohm

The kits are available for:

US$15 unassembled or US$20 assembled

https://shop.kit-projects.com/index.php?route=product/product&path=59&product_id=120

Reference

An interesting i2c encoder board for managing multiple encoders

John Scherer came across an interesting, i2c addressable rotary encoder board that allows you to connect encoders in just about any configuration.

The board has pins for digital or ADC I/O, has 256 bytes of eeprom, pads for setting each encoders i2c address, and works from 3.3 – 5V DC.   For something like the µBitx, this could be an easy way to add additional physical I/O (i.e. knobs).

There is also a video that gives a pretty good overview of how they work.

John VK2ETA suggests that on a read of the manual it appears the 256 registers are at one I2C address, and are divided between control registers and EEPROM addresses (two banks of 128 bytes).

The current implementation has the current modes for the encoder:

A. Relative, where the counter keeps the number of steps since last read. Reading it resets the counter to zero. Useful for frequency tuning in our case.

B. Absolute
B1. Without limits.
B2. With user defined limits
B2.1. No wrap around, like a potentiometer, hard stops at the limits.
B2.2 With wrap around, goes back to low limit if high limit is exceeded and vice-versa.

The encoder push button events are:
– button down
– button up
– double-press with user selectable double-press interval.

Current consumption is listed at less than 2mA plus LED current if used.

The board mounted PIC controller’s program is open source so it can be customized as well.

Tom, WB6B believes they keep a counter in the PIC chip that is on each board, so each time you check the status of an encoder board it will tell you how many encoder pulses took place since the last time you polled the data. This should greatly relax any timing issues.

Reference

Kit Projects selling outboard relay mod kit

David N8DAH from Kit-projects is marketing Gordon Gibby’s outboard relay mod as a kitset or for $5 more as a built-up board. This includes the circuit board, and all parts (including relays, diodes, inductors and caps).

Cost might seem high but David assures us he will be using quality parts.

The pre-orders were snapped up pretty quickly, but new stock will be coming shortly once the pre-orders have been shipped.

https://shop.kit-projects.com/index.php?route=product/product&path=59&product_id=119

Reference