Saturday, 29 October 2016

BASIC Tech Group - MyNews 2 - Freq Meter

This project has been abandoned as the accuracy is too low

Natively the Arduino UNO can use its timers to count up to around 6MHz. This can be extended up to a more useful 60MHz by using a divide by ten pre-scaler, for example the CD74HC4017 chip.

Here's the schematic for a FREQ_BASIC shield, it uses a 2 line by 16 column I2C Serial LCD display:

Screen Shot 2016 10 29 at 18 07 27


// FREQ-Basic, v2, Input Pin 5


// this LCD has an address of 3F, some others use 27. 16 columns, 2 rows
#define LCDADDR 0x3F
#define LCDCOLS 16
#define LCDROWS 2

// lcd object

// count result, and Arduino crystal correction
unsigned long count;
float freq;
float corr = 0.99852;

void setup() {


void loop() {
  if (FreqCount.available()) {
    count =;
    lcd.setCursor(3, 0);
    freq = (float)count * corr / 100000; //
    lcd.setCursor(3, 1);
    lcd.print(freq, 3);
    lcd.print("MHz     ");

On test with Arduino Si5351 DDS VFO on the left

IMG 0391

Accuracy is better than +/-500Hz, so not so good for accurate readings or frequency calibration, But OK for a general purpose indicator.

Thursday, 6 October 2016

BASIC Tech Group - MyNews 1 - Concept & Basic

VFO-Basic and DCRX-Basic

Last year we made a DDS in the "Concept" program, this provides us with an Arduino shield for frequency synthesis from 100kHz to 250MHz, SDR IQ outputs and a real time clock.

Screen Shot 2016 10 06 at 10 34 07

New BASIC project

The list of possible boards in the project is:

1. VFO - A 40m Basic VFO along the lines of that needed by the Amateur Radio Intermediate course. Introducing a Colpitts serial tuned oscillator with vari-cap tuning and an output buffer stage.

Screen Shot 2016 10 28 at 11 42 24

Eagle files can be downloaded here Schematic, Board.

Screen Shot 2016 10 28 at 11 42 40

2. DCRX - A 40m Basic Direct Conversion Receiver for CW and SSB, based on the world's simplest circuit using the SA612 mixer and LM386 audio amplifier.

Screen Shot 2016 10 06 at 10 24 21

Screen Shot 2016 10 06 at 10 24 46

Eagle files can be downloaded here Schematic, Board

Combined together the VFO and DCRX it makes a simple receiver for 40m, with manual or Arduino software tuning.

Here are the input filter LTSpice simulations:

Screen Shot 2016 11 13 at 21 02 12

Screen Shot 2016 11 13 at 21 02 18

Combined with the DDS frequency synthesiser board of the previous CONCEPT project, instead of using the VFO, the receiver can be tuned to an accurate frequency in the 7MHz band.

Here is the DDS & DCRX in operation, with WSPR signals being received on 40m, with the RX output fed to a Startech ADC running at 16bit/44.1kHz and fed to the WSPR program running on my iMac.

Screen Shot 2016 11 15 at 15 46 51

Screen Shot 2016 11 15 at 15 47 56

IMG 0460

IMG 0461

3. Future projects which are just ideas today and would be developed by members include:

- RFMETER - An RF measurement meter, measuring -80 to +10dBm. Update see later posting for completed design.

- BRIDGE - An Antenna Analyser, basically a 50 ohm bridge that shows the antenna impedance and SWR. RF input from the VFO or DDS

- QRP_RIG - a complete SDR based QRP TX RX

- WSPR PA - a 2W PA for 40, 30, 20m for a WSPR beacon.

- BPF - a switchable 40, 30 20m BPF board that can be used with the RFMETER and QRP_RIG

... and as many other ideas that members have. As an aside have a look at this web site by PY2OHH for a combine measurement system, similar to a combination of our boards stacked on our Arduino UNO. Could give some inspiration.