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Build Log: Bitx40 in the Case

I’ve had the surface mount (nearly assembled) version of the Bitx40 in a box since late last year. Its been a struggle to find a case that some room for expansion, but can still be used in the field. I settled on a Hammond 1598CSGY. The case is “instrument” style and has removable (and replaceable) front and rear aluminum panels.

My modifications to this so far are:

  • Rear BNC antenna connector
  • Anderson PowerPole connector
  • Upgraded heatsink
  • Bourns 10K potentiometer for volume control
  • Toggle switch for power
  • Nine pin Kenwood connector for the mic

I’ve verified the analog VFO works. It is too touchy without a geared or ten-turn potentiometer to control the frequency. I’m going to use my own DDS system. Probably built on an Atmel ARM and Si5351.

bitx0 copy bitx0

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Hands-on with the Asus Tinkerboard

When the Asus Tinkerboard came available on Amazon, I decided to go ahead and buy one.

I really like the color coded GPIO header. I have not tried to access the GPIO pins yet. That will come soon. The Tinkerboard does run much hotter than a Raspberry pi. My Tinkerboard came with two heat sinks. I bought a Smraza branded rpi case on Amazon that has a fan. One of the screws needs to be left off the fan as it sits directly on top of the heatsink.

The first version of TinkerOS I installed (1.4) would not boot after updating packages. I flashed the kingston micro sd card with 1.8 beta, and it is much more reliable.

Just for kicks I installed cpu scrypt mining software (just like with the Raspberry pi 3) to see how fast the cores work. Across all four cores, I see four to six kilo hashes per second. In my experience this is roughly twice the speed of the rpi 3.

 

blog0 copy blog0 copy1 blog0

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Pushing a MAX11115 8 bit ADC on the Raspberry Pi 3

I’m working up a Raspberry PI 3 add-on that gives the user a single 8 bit A/D channel. Over the last week I tried pushing this $2 adc chip as fast as possible via bit banging (no SPI here). Others have reported that they can toggle a GPIO pin fast enough to generate a clock in the high 20mhz range.

20khz at 600mv P-P

20khz

50khz

50khz

 

 

 

 

 

100khz

100khz

 

 

 

 

 

Here at 200khz you can see that data is starting to get lost
200khz

 

 

 

 

 

// The following code uses macros from http://elinux.org/RPi_GPIO_Code_Samples
for (samples=0 ; samples < kSampleCount ; ++samples)
{
GPIO_CLR = 1<<CS;

value = 0;
for (i=0 ; i < 16 ; ++i)
{
GPIO_SET = 1<<SCLK;
GPIO_CLR = 1<<SCLK;

if (i > 0 && i < 9)
{
bit = GET_GPIO(DIN) > 0 ? 1 : 0;
if (bit)
value |= 1 << (i-1);
}
}

GPIO_SET = 1<<CS;
sampleData[samples] = reverse(value); // Convert from MSB to LSB
}

 

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Build Log: Final Install of the MiniKits RF Amplifier

After the pcb was finished (minus the power MOSFET), the heat sink needs to be drilled and tapped for to mount the standoffs and the MOSFET pair. Source a 150x80mm heatsink on Amazn. The bottom is at least a quarter inch thick. I’m using M3-0.5 standoffs for all pcb mounting. It’s actually pretty hard to find a 2.5mm drill bit. I tried a metric tap set from Dubro, but snapped the bit in the first minute. I ended up purchasing a 40 pack (cheap imported bits). These bits performed way better.

minikits amp edit minikits amp side edit

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Build Log: RF Final Power Amplifier for the M1 Transceiver

I’m doing a lot of product R&D on my bench, so the M1 took the back seat for a while. I broke out the RF power amplifier kit. The EME210 is based on the RDF16HHF1 mosfet. The power amp assembled for me in about three hours. There are only a few surface mount parts on the bottom and about six inductors to wind. It comes with M3 standoffs and screws to mount to a heat sink. I purchased a 150mm by 80mm heatsink on Amazon.

m1_txvr_eme210_

 

 

 

 

 

 

I also spent the time to get the AGC/IF through audio amplifier stage aligned. At this point I really need logic control of the boards. I have a design for I2C based control of the system via the builtin 16 pin wiring harness. More on that soon.

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Bourns Optical Rotary Encoder Final Assembly

The new circuit boards for the break-out board I designed arrived. The assembled version checks out just fine with the interrupts enabled using the PJRC Encoder library.

I’ve struggled finding the perfect tuning knob to use this encoder on my [ongoing] M1 Transceiver build. Eventually, I decided the best thing to do would be to buy another Elecraft K3 tuner knob directly. Bottom picture shows it perfectly.

 

 

bourns rotary encoder back

 

 

 

 

 

bourns rotary encoder front

 

 

 

 

 

 

 

 

bourns rotary encoder mounted

 

 

 

 

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I2C Controlled Tactile Buttons

Sparkfun carries these nifty LED illuminated tactile buttons (SKU COM-10439). The LED’s are controllable separate from the push button action. Using them for real projects is pretty hard, especially if you have a case. In order to solve this, I devised a circuit board that has mounting holes, so these can sit up on a case.

But why stop there? For each button, you use two pins on your MCU. Then you need additional parts to do debouncing, pull ups, etc. Add a MCP23008 I2C expander, and you can control several push buttons over an I2C bus. This chip operates from 3.3V and 5V. It has wide support in the Arduino community.

2button pcb 2button pcb back

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Si5351 PCB with Low Pass Filter

In today’s mail, the latest revision to my Si5351 board arrived from pcbs.io. For me, this board is really a prototype and proof of concept. It is a reusable building block. This module is streamlined I can import it into a larger design in KiCad, remove the headers, and go. The low pass filter is really designed for HF work. One could change the values and reformulate the lpf.

After the kids go to bed, I salvaged the parts from the last generation board and assembled one. It is always thrilling when it works right off the bat. This generation fixes a VCC problem, adds additional bypass capacitors, an extra [optional] header for using outputs two and three. Lastly, lots of markings (documentation on the board).

si5351 rev1b top si5351 rev1b bottom

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Evaluating the Si8540 Current Sense Amplifier

I needed a current sensor for another project. I found the Si8540 in Mouser’s catalog. It requires a very low resistance sense resistor. The output voltage is in the zero to 3V range. The Si8540 comes in a SOT-23 package and costs US$0.55/piece in single quantities.

si8540I fabricated a prototype board that has holes large enough to solder 14 awg wires for load and source. Like most of my prototype boards, this one had a flaw in it (as seen by the jumper). Including the pcb, this board cost me less than US$2.00.

 

 

 

Using a current limited supply and some high wattage resistors, I compiled the data to chart the performance over a 3 amp load. The low of end of the current sense is skewed. The datasheet talks about the typical error at 1% of Full Load being 5% to 10%.

Si8540 calibration