Some great mods from PH2LB

 

Lex PH2LB  wrote to uBITx.net to tell us about a page on his website where he describes his uBitx (V3) mods.   This is a very nice build, and he has some good ideas.   Check his page out here

http://www.ph2lb.nl/blog/index.php?page=ubitx-mods

In particular Lex has developed some custom firmware that firmware geeks may be quite interested in …

“Second mod : custom firmware”

Originally based on the v2 software but merged to v4.3 and updated to code to have a lower RAM footprint (usage of F(…) macro and strcpy_P) with about 50%.

Source files can be found here : https://github.com/ph2lb/ubitx4

Over the last few months there have been a range of ideas to boost mic drive output or to add compression.  Here’s a mod designed to work with a dynamic microphone …

“Fourth mod : dynamic microphone amplifier.”

Because I like to work with dynamic microphones, I added a dynamic microphone amplifier based on the microphone preamp designed by Javier Solans Badia, EA3GCY for his ILER transceivers.

There are a whole bunch of ways to add buttons. KD8CEC does this through paralleling up buttons with different series resistor values on the encoder analogue port).   Lex has taken a different approach that will be of interest to some constructors.   He uses a PCF8574 I2C encoder (like the backpacks for a 16×2 or 20×4 LCD display) and uses the existing I2C bus…

“Fifth mod : again adding extra buttons.”

Using a PCF8574AP I2C IO Extender and hooked it up to the all-ready existing I2C bus on the Raduino for more direct menu buttons. Needs the custom firmware to direct switch between bands with a PA bandplan limitation (also has FULL option) and Step size up and down.

 

Something that a number of constructors have done is to remove the 7805  and supply 5v to the Raduio using a separate 5v supply.  Most are using buck or buck boost modules, but Lex has used a P-MOSFET.   There’s a good description of his approach on his website …

“Sixth mod : removing 7805 from Raduino and reverse power protection.”

Relocating the 7805 is a good idea, but adding a reversed voltage polarity to a uBitx is a must. I used a P-MOSFETs for that (also link to good video about using P-MOSFETS for reverse power protection).

Finally, you may be interested in Lex’s use of the Manhattan style technique for PCB layout.  It can look very professional as per this example:

An improved reverse voltage protection circuit

With four components, and the on:off switch, Bill K9HZ provides the ultimate reverse voltage and over-current protection system for your µBITx.  The fuse protects the circuit from excessive current draw – so you won’t blow your finals when you wind up the bias too far and they try to go into thermal runaway.  The relay must be powered on to power your µBITx (and the switch must be turned on).  With the series diode in place the relay cannot turn on unless the power is wired up correctly.

What’s a safe operating voltage for the uBITx?

Bill Erickson asks, “Is it safe for me to use my current 13.8 v power supply on a ubitx, or do I need to pick up a 12 v 5a version?”

The answer is probably.   Many constructors have been using 13.8v supplies with the µBITx and the BITx40, and quite happily over a reasonable period of time.  The parts are generally rated to cope with 12v nominally, but this typically means up to around 14-16v.

There are components in the µBITx, however, that will not cope with more than 15v.  Some capacitors are 16v rated.  A component that is rated at a maximum voltage of 15v is the TDA2822.

Those of you with a WX version of the TDA2822 should be using a voltage regulator to reduce the voltage to 9v or less on this chip.   The chip is, otherwise, bound to fail.  Those with the FCI version needn’t worry so much, but may want to current limit (with a resistor) the output of the audio stage into speakers/headphones.

Reference

Variable power supply

One of the discussions on the BITX20 IO list over recent weeks has been a variable power supply to control power out on different bands.   This seemed like the wrong approach to addressing variable output of the µBITx to the editor of ubitx.net (where the problem of inadequate drive or inadequacies in the PA design should be addressed directly) until he spotted this circuit diagram drawn up by Walter W9KJO, based on earlier suggestions.     It is simple and straight forward with the TIP142 device at the centre of the “buck” function.   24v input can be adjusted downwards to set the power output of the µBITx PA stage.

Walter says, “It controls voltage nicely. Really helps limit output power while working digital.”

However the TIP 142 really generates some heat.  He has a heat sink on the device, but the heat sink will need to be much larger to be safe.

Reference

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
Diodes
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
D7 BT149G SCR
D8 BT149G SCR
D9 BT149G SCR
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
Transistors
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
Switch
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
Conectors
Your choice
Reference

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.”

Reference

Maximum Safe Input Voltage

Paul K0ZYV asks, “What is the maximum safe input voltage to µBITx?”

Paul has lithium ion batteries that provide up to 4.2 volt when fully charged, and he hoped to put four in a pack which could max out at 16.8 volts providing about 2300 maH to power the µBITx.

The consensus seems to be around 15v is the maximum voltage that should be applied to the µBITx.

The reason is that the audio amplifier absolute voltage limit is 15V. All the other components can handle the 15V voltage.  This assumes of course that the 5V regulator on the raduino has a heatsink and better still has a series resistor to limit power dissipation.

Regulating the voltage when using Lithium Ion Batteries

VE7WQ uses a $1.45 Boost Buck DC adjustable step up down Converter XL6009 Module with a 4 cell 18650 Li-ion Rechargeable Battery pack.  This has the following characteristics:

Wide input voltage 5V ~ 32V;
Wide Output Voltage 1.25V ~ 35V
Built- 4A MOSFET switches, efficiency up to 94%.

Reference

Anderson Powerpole chassis mounts

Dave WI6R showed off his aluminium chassis to the list, but this resulted in questions about how he mounted his Anderson 12v powerpole connectors.

The answer is that you can use either of these mounting systems (the second was used in Dave’s case):

#1 https://powerwerx.com/powerpole-connector-chassis-mount-4

Note, that the mouting clamps do not have to be mounted on the exterior of an enclosure.  They can just as easily be mounted on the inside, making the who affair look more presentable.
Reference