Teensy audio board schematic and simplified audio “board”

Dr Flywheel (aka Ron N7FTZ) has provided some details of the Teensy audio add-on board.  This is used in the upcoming JackAl add-on board expected to be available shortly, but can almost certainly be home-brewed by savvy constructors using the Teensy 3.6 and audio add-on board.

Here is the circuit diagram for the PJRC audio module:

The CODEC part is very much the reference design provided by the part manufacturer. The support for the EEPROM and the SD card is optional.

The libraries will be compatible with any SGTL5000 or for that matter a long list of other I2S compatible CODECs (look at the source code). If you are homebrewing an audio processor on the Teensy you should consider integration of the CODEC. The libraries will support the internal A/D-D/A of the Freescale ASIC with very few components (resistors, capacitors) added.

Sample resolution of 12-bits is sufficient for the type of audio DSP that we need, though the higher bit-rate CODECs are much better. It is a matter of cost effectiveness and board space.

An alternative simpler approach


Below shows mono circuits for a lower grade Teensy, however the circuit is the same for the Teensy V3.6 with the corresponding pins.

The input circuit (mono):

Here is the output circuit (mono):


Warning for those using a Teensy 3.5 or 3.6 or Biteensio board

Jim Sheldon, W0EB notes that the tiny power jumper on the back of the Teensy 3.5 or 3.6 MUST be cut when using external power to the Teensy (from the BITeensio board). Left intact, it is possible to have power being applied to the Teensy through BOTH the BITeensio board AND the USB connection, especially during programming or remote control operation via the USB port. This may cause board power and USB power to conflict with each other and can destroy the Teensy.

The jumper is pointed out on the back side of the pin-out card that comes with every Teensy and it states: “Cut to separate VIN from VUSB, if using a battery charger or external power.” with an arrow pointing to the jumper between the two pads.

Carefully cut this tiny jumper with a very sharp hobby knife to avoid any possible problems.  After cutting the jumper, you will have to power the board externally through the BITeensio card (or other means) when programming or re-programming the Teensy through the USB port.  This holds true for Teensy boards used in just about any application, not just on our BITeensio board.


Jack W8TEE has let the cat out of the bag

In an earlier news item on ubitx.net, we speculated about projects under development by various teams.   We speculated that Jack W8TEE was up to something that involved a touch screen display and a processor upgrade.  Well the cat is now out of the bag.  The photo below was post by Jack on the BITX20 list.  This is the display panel of the JackAl board that the team will release shortly.

Al (AC8GY) and Jack picked the Teensy 3.6 because of its horsepower, good FFT library, and audio processing board. Al’s doing an info piece on JackAl which should answer most questions about it in an effort not to chew up the BITX20 group’s bandwidth.

There was no “target date” originally for announcement of the project. However, when Jack was asked to speak at FDIM, the project team thought it would be “kinda cool to show it off” at the Homebrew Show-and-tell on Friday night (8-10PM), so the target became real.

Al and Jack are starting to look like slugs who haven’t seen daylight in about six months.  JackAl should be a fun board for a lot of people because its heart is the Teensy 3.6 which has lots of resources associated with it. Currently, we are using less than 10% of both flash and SRAM.

Jack says, “I hope to see a bunch of you at FDIM …”



Processor upgrade to a Teensy

Stephen, KD2NDR, has been working on porting the µBitx code to a Teensy.

He has added a few other features with the new expanded memory capability.  This includes an I2C 4×20 display, leaving many pins for other uses,  and digital beacon modes supporting all JT modes, WSPR and FSQ.   Transmission is triggered by a timer interval set through main menu.

The teensy real time clock is updated using a GPS module.   Stephen plans to add an option to set the clock manually or via a serial port at a later date.  His implementation also allows for dynamic setting of a maidenhead locator (4 or 6 character) based on the GPS data.

Planned features for a future build include an SD Card to store custom messages and logging for digital mode operations.   He also plans to provide numeric keypad support sot that text can be entered directly along with setting the frequency.   A voltage/ amps monitor for battery operation,  and an. swr meter, and more is planned.   Stephen promises to make the software available to constructors when he  gets more time to test everything in more depth.

In commentary on the measurement of amperage,  there were several suggestions for how to do this including the use of cheap “Hall effect” sensors.   Probably the best of these came from Arv, K7HKL, who suggests:

” An alternative approach for current monitoring might be available.  As part of a workbench system I built a dual-port DC voltmeter using an Arduino NANO.

“By using two ADC inputs I can measure voltage on both ends of a resistor and
the use the NANO software to calculate difference voltage.  This lets me

manually calculate the current from resistance and voltage.

“In a captive system this approach would work because the software would know the resistance value and thus be able to measure differential voltage and from that calculate current flow through that known resistance.

“Differential voltage measuring is necessary in cases where both ends of the device being measured are at some potential above ground, because the Arduino ADC can only measure relative to a ground reference.”


A processor upgrade – via a plug in to your Arduino Nano.

Here’s what the little Skunkworks from Jim N5IB in collaboration witih W0EB and W2CTX has been up to!

Jim says he has “A wee PC board that accepts a Teensy 3.5 or 3.6 processor, then plugs into the space that would have been occupied by a NANO”.

Corresponding I/O lines are routed to maintain compatibility with the uBITX. Since the Teensy has a RTC (real time clock) there’s a spot for its backup battery.

In principle, the adapter could be used to plug in a Teensy anywhere a NANO used to live. On a stock Raduino (you would have to remove the NANO and socket the space).  On an enhanced Raduino, such as the RadI2Cino (developed by N5IB/W0EB and W2CTX) it is simply a matter of inserting the plug.

The Teensy brings lots more memory, more I/O lines including lots of analogue ports, an on-card microSD slot, and of course a Real Time Clock.

The Teensy 3.5 runs on 3-6 volts, with 3.3V logic, but has 5 V tolerant digital inputs. The Teensy 3.6 also runs on 3-6 V, but its logic is 3.3V only.  It is faster and has more memory than the Teensy 3.5.

Prototype boards are in hand and will be beta tested within the next few days. Firmware portability is of course the thing that must be confirmed.

Jim promises to keep us up to date.


A complete top board for µBitx

Martin Held AE7EU has been very busy designing a top tier board for the µBitx main board.

The board interfaces via the standard connectors to the main board of the uBitx.  Martin’s top board adds essential features, such as speech compression, an integrated Teensy 3.2 processor, an attenuator and an auto antenna tuner.   The front panel break-off from the board simplifies construction and makes the form factor as small as possible.

We look forward to seeing Martin’s report on how the board performs in practice.  It is likely we will see a few changes to the board before it becomes available to purchase!

In a post to the BITX20 list Martin identified four options for release:

1) Release the board files, schematic, design files/gerbers, BoM and let someone in China clone it, walk away.
2) Same as #1, but just sell bare PCB’s.
3) Sell PCB’s with all SMT components installed, and a baggie of TH parts, toroids, and couple feet of magnet wire.
4) Sell the entire thing fully assembled ($$$).

It is likely that either options 2) and 3) will be favoured by the amateur community, based on initial feedback to Martin.