KD8CEC documentation

Ian Lee, KD8CEC has added further documentation on his website about his alternative firmware for the µBITx transceiver:

General features


Memory Channels

Reducing CW Key errors

You will also find additional resources on the website covering his AutoKey (built in software memory keyer), his uBITX Manager software and more.

Using the Adafruit si5351 Board

Many constructors are using the Adafruit si5351a i2c board with their µBITx as part of a Raduino replacement (often in conjunction with a processor upgrade and feeding the display with an i2c daughter board).

Note that the Adafruit board does not have 0.1uF capacitors on the outputs of the three clocks.   You will need to find a way to incorporate these capacitors in your circuit.

K9HZ Full Rig Power Control Unit

Bill Schmidt, K9HZ has  designed a fool-proof control circuit for the uBITx for power control.  This circuit prevents bad things from happening by shutting down the radio before any damage is done. 

It faults on:

  1. reverse voltage
  2. over power
  3. High SWR
  4. High PA Current 
  5. High voltage. 

It provides a visual indication of WHAT fault occurred, and the individual fault LEDs begin to flicker BEFORE the trip so you can fix the problem before you hit a hard trip. 

The fault conditions listed above can be expanded to any number by adding more SCR Trip components (they are set to trip at 1.8V whatever the fault is).

 When initially turned on, the transistorised RS Flipflop circuit comes up in the “Operate” mode.  If a trip occurs, it flips into “FAULT” and shuts down the PA. 

The circuit is reset with the “RESET” button, but ONLY if the fault has been resolved.  Turning the power off and on resets the circuit too.

Bill bread-boarded the circuit last week and has been using it on his radio for a while and found that it works flawlessly (yes transmitting and yanking the coax off the back of the radio shuts down the PA nicely!).  The circuit and a build list can be found in the BITX20 list’s files section.

Parts List for the uBITx Power Control Circuit

Capacitors Value Voltage
C1 10uf 16VDC
C2 0.01uf 50V
C3 0.01uf 50V
C4 0.1uf 50V
C5 0.1uf 50V
C6 0.01uf 50V
C7 0.01uf 50V
C8 0.01uf 50V
C9,C10, C11 0.01uf 50V
D1 Green LED
D2 1N4148/ 1N4001
D3 1N4148/ 1N4001
D4 Red LED
D5 1N4148/ 1N4001
D6 12V 0.5W zener 1N759, or 1N5242, or 1N6002
D10 BT149G SCR
D11 1N4148/ 1N4001
D12 1N4148/ 1N4002
D13 1N4148/ 1N4003
D14 1N4148/ 1N4004
D15 Red LED
D16 Red LED
D17 Red LED
D18 Red LED
D19 SB530
Q1 2N3904
Q2 2N3904
Q3 2N3904
Q4 2N3904
Q5 2N2222
Resistors Value Watts
R1 1K 0.125
R2 1K 0.125
R3 10K 0.125
R4 10K 0.125
R5 10K 0.125
R6 10K 0.125
R7 10K 0.125
R8 100K 0.125
R9 2.2K 0.125
R10 47K 0.125
R11 1K 0.125
R12 2.2K 0.125
R13 1K 0.125
R14 1K 10-turn POT
R15 10K 10-turn POT
R16 88K 0.125 Can just use a 100K POT set appropriately
R17 12K 0.125 Can just use a 100K POT set appropriately
R18 10K 0.125
R19 100K 0.125
R20 1K 0.125
R21 1K 0.125
R22 1K 0.125
R23 1K 0.125
R24 10K 0.125
R25 10K 0.125
R26 10K 0.125
R27 10K 0.125
R28 62 OHM 2
R29 1K 0.125
R30 1K 10-turn POT 0.125
R31 10K 0.125
R32 100K 0.125
SPST Momentary contact
Integrated Circuits
U1 LM339 (Make sure to connect Vdd and ground!!!!).
U2 BTS660P
Fuses Value Voltage
F1 1A Poly Fuse 50V
F2 4A Poly Fuse 50V
Your choice

Variable Power Control

Dave N4LKN has developed a potentiometer controlled version of his original zener power control.   He added high limit and lo limit resistors as illustrated in the circuit diagram below:

He says, “I will be adding a simple accurate circuit add on to this to report voltage and current supplied to the output stage using 2 analog inputs to my system health display.”


Debouncing a Rotary Encoder

N5IB reports, “ALPS, a maker of rotary encoders, recommends 10K pullup to Vcc, then 10K in series with 0.01 uF to ground. The internal pullup in the ATMega is loosely specified – somewhere in the tens of K, max 50K.

Jim Sheldon W0EB responded with, “This settled the really cheap and modified (to take the detents out) encoder on the test set right down. Tuning is extremely smooth and I don’t notice ANY digits showing up and then backing up again as it did before.

“I can highly recommend adding a 10K external pullup to both the encoder A and B inputs as well as an additional 10K in series with .1uF capacitor to ground on both the A and B inputs to the Raduino card.

“It was a nice surprise addition and I won’t leave them out again.”

Hans G0UPL responds, “Debouncing and pullups are also possible in the firmware. This is the method I use in the QRP Labs kits like QCX http://qrp-labs.com/qcx – look at the schematic: no pull-ups, no RC-debounce. Saves 6 components (4 resistors, 2 capacitors). It’s not important in a one-off build or modification but in a kit where you are trying to optimise cost, every resistor helps! The firmware method also gives you more control over how you do your debounce. I prefer the state-machine approach to rotary encoder handling, it implicitly debounces without involving any time constants.”


Guide to Arduino Coding

The best book around for learning how to program your Raduino was written by one of the BITX20 regular contributors Jack Purdum W8TEE.   It is entitled “Beginning C for Arduino”  and can be found on Amazon.

Jack says, “Make sure you get the 2nd edition…it’s a better book and has a chapter on C++ so you can “understand” most library code.”

KF2510 connectors on the uBITx

The connector type used on the main board of the µBITx and the Raduino are of type KF2510.  These were developed by MOLEX and are of the polarised and locking type with 0.1″ spacing between pins.  They are commonly available  everywhere.  In the US they are available from Tayda and Mouser.  In Australia and New Zealand they are stocked by Jaycar.  If you have time for delivery they can be obtained cheaply on AliExpress and Ebay websites, including in sets in a plastic storage box.

The KF2510 comes with both straight pins (for connectors to a board) and with 90 degree pins.  The 16 pin connector between the Raduino and the main circuit board uses the 90 degree type on the Raduino end, and straight female socket on the main board.

Connecting wires to the female connectors is straight forward.  Line up a section of wire (stripped back by around 1/4″) and use needle nose pliers to crimp the bottom-most crimp section first, and then the top one.   Most of us apply a dab or solder between the crimps to secure the wire firmly to the female pin.

The female pins just push in, but must be oriented correctly in order to be held firmly in the socket.  If they come straight out you are putting them in backwards.  The female pins are easily removed by pressing on the back of the metal pin with a flat-head screwdriver by reaching through the little window  and at the same time pulling on the wire.   Rather than curling up your spare wire connectors, it is better to pull them out of their socket for storage  in the junk box.  They can be reinserted when you want to use the connection again later.