Ashhar Farhan tells it as it is … the problem of the TDA2822

Ashhar Farhan VU2ESE, designer of the µBITx tells us the sorry saga of the TDA2822:

“Here is the story. This is going to cause a lot of heartaches. I chose TDA2822 after listening to a lot of bad press about the LM386. Upon looking at its harmonic distortions et al, it was found to be a reasonably good device. In, it went.

“Now, unfortunately, the TDA2822 production has entirely stopped. None of the standard suppliers, including mouser, newark, element14 have no stocks left. We tried to find other source of remaining stock from our reliable supplier who has been supplying to us in the past as well.

“He turned up with a batch. We tried the ICs in burn tests for. Ten of them on ten boards at full volume for a whole day. In retrospect, we should have tested every individual IC. That batch had these WX ICs as well. About 100 to 150 of these must have shipped, there is no way to know. The way it works is like this : Not all the ICs turned out by a factory are good. So work very well, some not so well, some don’t work at all. These wafers make it to the silicon industry underground where they are cut out from the wafers and packaged and sold as low grade versions of the same parts. We got a a hundred or so of these lemons.

“We finally located a source of brand new, high quality TDA2822s that are currently being shipped. They cost almost five times as much as we were paying while this was in production. Well, such is life.

“In the meantime, we have to look for alternatives to the TDA2822. I am highly inclined towards making a discrete device amplifier. We will never run out of discrete devices, the audio would be so much better. Does the gang have any ideas?”

Initial feedback suggests that there will not be a consensus reached on a replacement.  Some want to stick with the TDA2822 (assuming a reliable source of affordable devices can be found), some would prefer the ability to add in a module of the builder’s choice, and others would like to see the device replaced with discrete components.  David N8DAH suggests the drop in replacement –  NJM2073D-ND

Reference

KD8CEC minor firmware update v1.04

Ian Lee, KD8CEC, has released a further minor update of his firmware (v1.04).  You can download it here.

The changes since version 1.01 are as follows:
– Reduce cpu usage
– Change BFO Calibration step (50Hz to 5Hz steps)
– Change CW Frequency Display (frequency is more accurate when in CWL, CWU Mode)
– Optimized source code and reduced program size (97% -> 95%)

WA6ISP uBITx replacement Raduino

Mike Hagen, WA6ISP has previously supplied Raduino X and Raduino XP alternatives to the builder community for the BITx40 units.    He has been asked by many builders whether a µBitx Raduino replacement was planned.

He now has designed, built and tested a µBITx Raduino replacement.  This comes with the extra feature of having an i2c 16 port I/O expander on board. The Microchip Expander IC uses the Adafruit Library MCP23017 to create 16 more Digital Pins.

This replacement board is slightly bigger than the standard Raduino and has the Ardunio Nano facing towards the left rather than to the right.

Email Mike for further information or to order.   The cost of the bare board is US$12 and the built up board is $46.  Note that the bare board will require you to source all parts and  mount some fairly small surface mount devices.

µBITx constructors now have several alternatives to choose from in considering a replacement Raduino board: the WA6ISP uBITx Raduino, the W0EX Radi2cino and VK4PLN Raduino replacement.

External speaker and headphone jack

Generally speaking, internal speakers in a QRP transceiver, like the µBITx will be inferior.  Fragile, rattly and thin sounding, and inefficient.   Don Cantrell, ND6T, has written an article about how he dealt with this problem.  He incorporates a headphone jack in the speaker with a switch and an associated signal limiter circuit to prevent the RX from damaging his eardrums with loud stations and static bursts.

See his blog page for details.