GPS Connection to Hans Summers Ultimate 3 QRSS Kit

A few years back I built a QRSS transmitter (for slow morse and WSPR) based on a recycled DLink DSL-502T router running OpenWRT and connected to an Si570 DDS module. (http://www.quicktrip.co.nz/jaqblog/home/44-si570qrss)

This worked well for a while but eventually the DSL-502T failed and would no longer connect to the network.  Not great for a time synchronized QRSS transmitter that relied on NTP service.

The replacement is a Hans Summers Ultimate 3 QRSS kit.  (http://www.hanssummers.com/ultimate3.html).  The Ultimate 3 is a combination microcontroller and AD9850 DDS module that if connected to a GPS providing 1PPS and $GPRMC NMEA sentences will generate time synchronized messages in a number of formats with no requirement for network connectivity.

In my parts bin I had several Ashtech g8 GPS modules.  The Ashtech g8 is a late 1990's GPS module designed for integration into OEM equipment.  I picked up a several at an Amateur Radio junk sale a few years back and hadn't really put them to use.

The g8 meets the requirements for the Ultimate 3 by providing the required 1PPS signal and $GPRMC sentence.  Unfortunately the default configuration on power up does not send $GPRMC and instead sends $GPGGA and $GPVTG at 4800 baud.  The startup configuration can be changed by connecting via the serial interface, changing the configuration and saving to backup memory but to retain this (and the GPS almanac for fast power on) when the power is cycled requires a 2.7v-5.5v power source on the V_BACKUP line.

With fast startup not critical for this application and not wanting to worry about backup batteries going flat, I decided to go with a different approach and use a microcontroller to reconfigure the g8 on power up.  

With a number of other applications for GPS in the shack I also decided to buffer the 1PPS and Serial outputs of the g8 and make these available for use other than the Ultimate 3.  This is done using a standard 74LS buffer.  More on this in the next article.

The GPS configuration is handled by an AVR ATTiny2313A with the code written in C using AVRStudio with the compiled code using 508 bytes (28%) of the available flash memory.

The approach is as follows:

  • Wait 5 seconds on startup for things to settle
  • Start receiving serial data from the GPS at 4800 baud looking for 0x0D, 0x0A,$ indicating the GPS is in the default configuration sending data at 4800 baud
  • Configure the GPS to send data at 9600 baud using the command $PASHS,SPD,A,5
  • Start receiving serial data from the GPS at 9600 baud looking for 0x0D, 0x0A,$ indicating the GPS speed configuration command worked correctly
  • Configure the GPS to stop sending $GPGGA and $GPVYG (actually stop all data) using the command $PASHS,NME,ALL,A,OFF
  • Configure the GPS to start sending $GPRMC using the command $PASHS,NME,RMC,A,ON
  • Sleep

I have included the code here should it be useful for anyone wanting to perform similar configuration but note that your GPS may require different commands.

 

ATTiny2313A and 74LS buffer.  The ATTiny2313A can be run from an internal oscillator with no external crystal and capacitors required but they were already on the board after an aborted attempt to get C code to run correctly on old AT90S2313 parts from the junk box.  The LED's are for debugging and indicate the current state machine step.

Alternate view showing the Ultimate 3 and the g8 GPS module.

 

TRS80 Model 4P FreHD Installation

Following on from the post about the Model 4 FreHD installation, here are a few pictures showing the installation of a FreHD Hard Disk Emulator in my TRS-80 Model 4P.

The mounting chassis is the frame from a dead Miniscribe 8425 hard drive.  The FreHD is mounted on a piece of plastic attached in the drive frame.

The FreHD is connected to the Model 4P expansion connector with a long 50 way ribbon cable.  Installation required a lot more disassembly of the machine than for the Model 4. The ribbon cable routes from the expansion connector across the 4P motherboard and comes out at the front of the chassis (but inside the plastic case) before it can get into the drive bay.

An SD Card extender (available on eBay) was used to make the SD Card accessible outside the Model 4P case. In this installation the SD Card socket is accessible in the modem port bay at the back of the 4P.

 

 

FreHD in recycled Miniscribe Drive Chassis

4P front view replacing a 5.25" Floppy

4P rear view showing SD Card slot and expansion cable

 

 

TRS80 Model 4 Internal FreHD Install

A few pictures showing the installation of a FreHD Hard Disk Emulator in one of my TRS-80 Model 4's.

The mounting chassis is the frame from a dead Seagate ST4766N hard drive.  I picked up a box of these in the early 2000's and that sat in the corner of the workshop waiting for a project just like this.  The FreHD is mounted on a piece of plastic attached in the drive frame.

The FreHD is connected to the Model 4 expansion connector with a long 50 way ribbon cable.  Installation required removal of the Model 4 PCB so the ribbon cable could be routed between the PCB and the metal chassis frame.  The cable comes out at the top of the Model 4 chassis and then attaches to the connector on the FreHD.

An SD Card extender (available on eBay) was used to make the SD Card accessible outside the Model 4 case for the few times I want to change the installed software.  I don't change the software on the cards often so having the SD card accessible from behind the machine rather than from the front isn't really a problem.  The SD Card extenders work well but the FreHD doesn't recognize that the card has been removed and inserted because it relies on a physical switch on the SD Card socket.  Best practice is to power down the machine before changing the SD Card if you use an extender.

FreHD installed in Model 4 Drive Bay. Expansion cable visible.

Alternate view showing SD Card extender cable

Not as shipped from the factory but a tidy installation

 

 

Computer Specialists Ltd - CS-16/64 Single Board Computer

A while back I was given a Z80 single board computer by Keith (ZL1BQE) when he found out that I really liked the Z80 microprocessor.

The board was made in New Zealand by Computer Specialists Ltd and sold as a "controller".  Apparantly it was also sold as a basis for a complete Z80 machine with a disk controller and could run CP/M.

I don't know the history of this particular board.  There are hand written comments on the documentation about "Pye TV's" and "Sheraton Rotorua" and I had an email discussion with Mark Eaton at Compuspec (the manufacturer still exists) and he said some of these boards were used to drive information screens in hotels.

I only have the main PCB (not the video or disk controller described in the documentation) which had been burgled for a few parts but thanks to the documentation it was actually pretty easy to get going.

It needed a replacement 4.9152 mhz xtal for the STC (AM9513 System Timing Controller).  This is used for the real time clock but more importantly the timing clock for the SIO/0 (Z80 SIO/0 serial IO controller).  Also a clean up around the reset circuit.  Looks like a reset switch or something was removed so the board by someone with a plumbers soldering iron so it wasn't in great shape there.  

The serial level converters needed to be replaced (MC1488 and MC1489) although they may never have been fitted because the serial port CTS pullup resistors were not fitted to the board (more on that below).

It took some digging into the ROM to work out why the CPU seemed to run and the STC was configured to generate the correct SIO clock frequency but nothing appeared in the terminal.

Two things.... the console is actually on port B of the SIO (not directly stated in the documentation although implied by the pinout on the serial header).

Also because the CTS pullup resistors were not fitted.  These pull the CTS lines at the serial connector to +12V which is inverted by the MC1489 to be "active low" for the SIO /CTSA and /CTSB signals. Without the resistors these signals are +5V and the SIO won't transmit anything.

So it works. Monitor ROM and Tiny Basic both run and work as documented.

 

Documentation for the CS-16/64

Technical Manual Schematic for CPU Board Schematic for Video Board Layout for CPU Board Schematic for Memory Board

 


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Contact Andrew Quinn

jaquinn@ihug.co.nz http://twitter.com/jaquinn