Sequencer with variable delay

This page describes my homemade sequencer. It controls the different components in my EME station.

Function

overview
Fig. 1. The sequencer (yellow block) controls my 2 meter EME station.

Figure 1 shows how the sequencer controls the hardware. Three events must take place in specific order when PTT is activated and the system switches from RX to TX.

  1. Disable the preamp (remove 12V from port 1)
  2. Change RL1 and RL2 from RX to TX (port 2a/2b)
  3. Enable the PA (port 3)

When PTT is deactivated, the system switches from TX to RX. The events are now executed in reverse order.

  1. Disable the PA (port 3)
  2. Change RL1 and RL2 from TX to RX (port 2a/2b)
  3. Enable the preamp (apply 12V to port 1)
Figure 1: When WSJT commands the transceiver to change from RX to TX, it activates the transceiver's PTT line. The STBY port follows the PTT line immediately. WSJT will delay the audio 200 ms (defalut value). This delay can be configured in WSJT (Settings > Advanced > TX delay). I've set TX delay to 300 ms.

delay skema
Fig. 2. Events and delay.

Figure 2 above shows how Event1 must finish before Event2 begins, and so on. The 100 ms delay in figur 2 may not be optimal for everyone. If 200 ms delay is required, the user fits jumpers for 10 decimal and then resets the Arduino Nano. The delay is now 200 ms. 

Circuit Diagram

circuit diagram
Fig. 3. Circuit Diagram.

The heart of the sequencer is the Arduino Nano. Three digital pins (D06-D08) are used for controlling the LEDs on the front panel, and D09-D11 are controlling the output ports. The pins D02-D05 are used for setting a binary number which decides the delay in milliseconds. The delay range is from 20 ms to 300 ms in steps of 20.

delay table 
Fig. 4. Delay is set using jumpers.

Panel meters M1 and M2 monitor the current flowing through Port1B and Port2B. Both ports supply power to equipment mounted in the antenna mast (preamp, RL2). I like to keep an eye on their power drain. Each unit use about 150 mA when active.

Hardware

Most discrete components are fitted on a Veroborad (stripboard). Some components are soldered directly onto the BNC-sockets on the rear panel.
 
Veroboard
Fig. 5. The populated PCB.

front
Fig. 6. Front view.

rear view
Fig. 7. Rear view.

sequencer seen from above
Fig. 8. View inside the sequencer.

Software

The software is an Arduino sketch (sketch = a file containing source code). The sketch is imported into Arduino IDE, compiled, and uploaded to Arduino Nano via the USB-port.
This file contains the sketch for the project: sequencer_oz1bxm.zip
Written by OZ1BXM Lars Petersen 17-Oct-2017. Revised 15-May-2019.

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