Melt Solder DDS Controller

A multiband QRP transmitter using the NJQRP DDS Daughtercard

Steve “Melt Solder” Weber is a master with the ATmel controller chips and he’s designed a circuit with the NJQRP DDS Daughtercard that is super feature-rich. The project serves as a multi-band QRP transmitter on the HF ham bands, with paddle input, dual-memory keyer and speed control, programmable IF offset, EEPROM-stored settings, RIT and XIT split mode operating, LCD display, Rx mute, Tx sidetone generation, and logic to drive an antenna selection relay … Wow!

The MS-DDS controller can be built on a pc board available from the AmQRP Club or even on a small piece of perf board. One with solder pads would be ideal. Most of the connections are made off the board, so only a few components need to be wired up to the controller chip. The board can be cut down to the outline of the LCD display and mounted to the back of the display by using single inline package (SIP) pins and sockets.

Using another SIP connector, the DDS Daughtercard can be plugged directly into the microcontroller board as shown in the photo. This arrangement makes for a compact transmitter module. Otherwise, the DDS module may be mounted elsewhere in an enclosure, but try to keep the connections to the board less than 6″ long. If possible, use ribbon cable. Keep the lines short, as long cables may result in improper operation of the DDS chip.

Small “TAC” switches are a good choice for the push buttons. They are inexpensive and have minimal bounce. The ones pictured on my board are from Mouser (p/n 612-TL1100F).

A 2×16 (2 lines of 16 characters) LCD display module is required. Nearly all LCD modules use the same pin assignment and control codes, a standard set by Hitachi many years ago. Those stating use of the HD44780 controller chip will likely work fine; however, some very inexpensive surplus displays may not be compatible. LCD modules can come with three possible locations for the connecting pins: top, bottom and side. Try to get one with the connections along the top edge of the display, as this will mate best with the pin out of the controller. Also, a display with an LED backlight is highly recommended, despite the additional cost, as these are much easier to see at night. The display used in the unit pictured is the Seiko L1682 (available from Mouser, p/n 628-L168200J)


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