I recommend building the Display and Control Board, and Keypad Board following the Power Distribution Board. Building these boards next provides the capability to test and exercise each of the the receiver subsystems as they are subsequently built.
The Display and Control Board contains a Microchip PIC18F45K22 high performance microcontroller that is used to implement Express Receiver display and control functions. The ExpressPCB MiniBoard service provides 3 boards. All three boards are used in the Express Receiver to implement a Main, Left and Right Display and Control Board as shown in the Display and Control Board Interconnection Diagram below.
The I2C bus is used to interconnect the three Display and Control Boards. The Main Display and Control Board is the I2C bus master, and the Left and Right Display and Control Boards are I2C bus slaves. The I2C bus also connects various Express Receiver subsystems with the Main Display and Control Board as shown in the diagram above.
The Main Display and Control Board provides the following interconnection functions.
I2C Bus Master
Drives the Main LCD which displays VFO A and B frequencies, and memory frequencies.
Keypad Board scanning via parallel I/O lines. Keypad rows connected to J1, and Keypad columns connected to J5.
Main tuning implemented via an optical shaft encoder connected to J4.
Selection of either the Si570 VFO or LO via a parallel I/O line on J2.
RS485 Serial I/O via J10 for interface to the Express Transmitter (future).
The Right Display and Control Board provides the following interconnection functions.
I2C Bus Slave
Drives the Right LCD which displays Express Receiver subsystem status information.
IF Bandwidth: 2100-, 1800-, 500- or 250-Hz
Tuning Rate: 1000-, 100- or 10-Hz
RF Attenuator: 0- to 30-dB in 2-dB steps
RF Amplifier: ON or OFF
Band: 160, 80, 40, 30, 20, 17, 15, 12 or 10 meters
Mode: USB. LSB or CW
AGC: Slow, Fast or Off
Audio Mute: On or Off
TX Lock: On or Off (future)
Control lines for the AD9835 DDS BFO on the BFO, Product Detector and Audio Board via parallel I/O lines on J5.
RF Attenuator and RF Preamp control via an optical shaft encoder connected to J4. Normally the RF attenuator is set to 0dB and the RF preamplifier is set to OFF. Turning the optical shaft encoder CCW increases the RF attenuation in 2db steps from 0 to 30dB. Turning the optical shaft encoder CW from the 0dB position turns ON the RF preamplifier, or decreases the RF attenuation by 2dB if RF attenuation is greater than 0dB. If the RF preamplifier is ON, turning the optical shaft encoder CCW turns the RF preamplifier OFF.
The Left Display and Control Board provides the following interconnection functions.
I2C Bus Slave
Drives the Left LCD which displays S Meter readings. The S Meter reads from S1 to S9; and +10dB, +20dB, +30dB, +40dB, +50dB and +60dB over S9. Instantaneous S Meter readings are displayed as horizontal bars. S Meter peak analog values are displayed above the bars and held momentarily on the display.
The ExpressPCB .pcb file for the board is here: Display and Control Board Final.
Refer to the RF Band Pass Filter page for information on the connectors J1 & J2, and J4 through J11.
J3 is a 6-pin section of breakaway pin headers, Sparkfun PN PRT-00116. J3 is designed to accommodate the Microchip PICKit 3 programming adapter which will be required to program the Display and Control Boards, and the IF Amplifier and Digital AGC Board.
J12, the LCD connector, is a dual in-line, 18-pin header, Mouser PN 649-77313-101-18LF. The mating connector housing is Mouser PN 571-104482-8 with crimp contacts Mouser PN 571-1-104479-3. Note, only 16 of the 18 pins are used on this connector.
All 0.1uF capacitors are SMD 1206 style chip capacitors.
C10 is a 1.0uF 20%, 25V tantalum capacitor in a 1206 SMD package, Digikey PN 493-2387-1-ND.
All resistors are 1/8W 5% SMD 1206 style chip resistors. For example, Digikey PN P10KECT for the 10KΩ resistors.
VR1 is 1KΩ trimmer in an SMD package and is used to adjust the contrast of the LCDs. Digikey PN 3361S-102GLFCT-ND.
LED 1 & 2 are clear green and red LEDs, Mouser PN 645-598-8270-107F and 645-598-8210-107F, respectively.
U2 is a Maxim MAX1482 RS-485 Transceiver that will be used in the future to provide a control link to the Express Transmitter. Digikey PN MAX1482CSD+-ND, 14 SOIC SMD package. This part along with C8, R8 & R9 are only required on the Main Display and Control Board.
U3 is a 7805CT linear voltage regulator in a TO-220-3 package. Mouser PN 512-LM7805CT.
Y1 is a CTS 25-MHz, 50ppm standard clock oscillator. Mouser PN 774-MXO45HST-3C-25.0.
The 3 LCDs used in the Express Receiver are blue, 20 character x 4 line LCD character display modules from New Haven Display. Mouser PN 763-NHD-0420DZNSWBBW.
The New Haven Display LCD modules have 16 through-hole connections with a pitch of 0.1″. Connections to the LCD modules were made using a combination of Molex rectangular connector headers: 1 x 6-pin, 2 x 4-pin and 1 x 2-pin, see photograph below. Refer to the RF Band Pass Filter page for information on the connector headers. It’s a tight fit when the connector housings are plugged into the LCD modules, but entirely workable and preferable to soldering wires directly to the LCD modules.
The main tuning control uses a Honeywell optical rotary position encoder. The part chosen has a very smooth rotary action (no indents) desirable for the main tuning, Digikey PN 601VCS-ND. A 1.75″ diameter TE Connectivity knob with a finger indent is used for the main tuning, Digikey PN 450-1703-ND. These two parts are relatively expensive, however, as the main tuning is the most frequently used control on the Express Receiver, they dictate to a large extent the “feel” of the receiver.
The RF Attenuator and RF Preamplifier control is via a Bourns optical shaft encoder, normally open switch with 18 indents, Mouser PN 652-PEC11-4125F-N18. The indents are desirable in this control application as specific RF attenuator and RF preamplifier functions are being selected.
© 2014 – 2015 Rod Gatehouse AD5GH