After a painful few days programming, trying to identify why I couldn’t do a simple thing like load SRAM with data, I found that I’d mis-typed one of the port names in the init routine. After editing the single character that was incorrect, it sprang into action!

I quickly modified the program to load a ‘proper’ Z80 routine and tried it out. It was a simple program, loading 50 bytes of RAM positioned just about the main code with a value. I first ran the AVR code to load the Z80, then manually switched off the /BUSRQ line (a modification I had to hardwire to the board) and reset the Z80. I then ran a read program on the AVR and the value I’d chosen was there in the SRAM! I changed the value a couple of times and re-ran the test to verify it was working.

;Z80 Test Program

DESTINATION_SIZE equ 50
.org 0000h
start:
LD HL, Storea                                    ; point to the source
LD DE, Storea + 1                              ; point to the destination
LD BC, DESTINATION_SIZE – 1      ; copying this many bytes
LD (HL), 170                                      ; put a value in the 1st pos
LDIR                                                  ; move 1 to 2, 2 to 3…
Finish:
NOP
NOP
NOP
NOP
JP Finish                                              ;Infinite Loop
Storea:
DEFS 50

end

The next step is to re-write the loading program entirely, in a more tidy manner, and test the Z80 properly when the two missing chips for the output port are delivered.

I’d like to say a big thank you to Bill Rowe who gave me some great advice and suggested ideas as I went along. I’m sure I will find his help invaluable in the future as I develop the ZAViouR Board.

For those who would like to follow the progress as it happens, I have a Hackaday.io page devoted to the project. You can find it at: Hacakday.io

In the video you can also see the hard-wired /BUSRQ switch which will be re-routed to the AVR in the next version of the board. The next version of the board will have improvements based on experiences with the current version. It will have 64Kb of SRAM and the address lines will be driven from the AVR via a port expander. This will free up plenty of AVR GPIOs for other tasks.

Lately, I’ve been distracted from general AVR stuff by the now ubiquitous ESP8266. I purchased a few ESP-01 boards and an ESP-03 board a while before moving location and I’ve just got around to learning a little about them.

The first thing I did was rig up a small strip board PCB to aid in the programming. At first, I was powering the ESP module from the USB to Serial adaptor but I found that it wasn’t man enough. I modified the board to accept external power from my bench PSU and disconnected the +3.3V line from the adaptor.

ESP-01 Prototype Programming Rig

This was just intended as a quick solution until I designed a proper PCB. Meanwhile, I discovered that you can use the Arduino IDE to program the ESP modules. I’m very familiar with the Arduino IDE so I installed the files required after downloading the latest Arduino software.

Having gotten interested in the ESP modules, I did some searching and one of the websites I came across was www.openhomeautomation.net Here was documented a way of logging Temperature and Humidity from a DHT11 unit connected directly to the ESP-01 module. You can see a DHT11 in the previous image in the top left of the PCB. I duly followed the instructions on the Cloud Temp/Humid Logger page and lo and behold, I had Temperature and Humidity values displayed on Freeboard (May not be up to date or accurate).

Although I had made the prototype configurable for programming and reading from the DHT11, I really wanted a dedicated board I could use, and one that would allow me to utilise the ESP-03 module that has lots of GPIO pins broken out. I set to work designing a board in Eagle.

ESP8266 Flash Board v.1.3 Eagle Preview

This is the result. A general purpose board able to accommodate either the ESP-01 or ESP-03 modules. The power source is selectable from either the USB to Serial input header or a Micro USB connector/standard 0.1 pitch header. In the latter case, the voltage is regulated to 3.3V by the LM1117T device. The board also features a 3.3V zener diode on the RX pin of the modules to prevent over voltages over serial, a reset switch, power indicator LED and GPIO header.

Once the boards have arrived from the fabricator and I have checked them over, the design files will be available on a dedicated page licenced under Creative Commons Attribution – Share Alike v4.0 for anyone to use as they see fit.

Way back last year, before all the hassle that moving location entails, I started to design a minDUINO variant to work with the UKHASNet mesh network. Finally, having gotten settled down, to a degree, in my new location on the south coast of England, I have been able to continue.

I have designated the new board as minDUINO v1.6b. The major difference to the previous boards is that it runs on 3.3v rather than 5.0v. It utilises an LM-1117T regulator. Apart from that, it’s pretty much the same as versions 1.5, 1.6 & 1.7 apart from the additional resistor network, an ESP8266 WiFi module and an RFM69HW module for radio duties.

MinDuino v1.6b UKHASNet Node

The RFM69HW is integrated on to the main board and the ESP8266 plugs into the header at the top of the board next to it’s associated component C10. Being based on the minDUINO, it retains all the programming and GPIO headers. I have added a header to access the RFM69HW’s GPIO ports as well. JP9 gives access to monitor the supply voltage pre regulator by connecting Vin to ADC0 on the ‘328 micro-controller and JP5 connects an optional indicator LED to D10 which the previous versions were hard-wired for. On the latest iteration of the board (not shown), there are also two through-hole test points to monitor the regulated voltage.

I have found it useful in the past to let a design sit for a while so that my brain can view it afresh and spot any glaring mistakes. My intention is to do so before having some PCBs fabricated by Hackvana. Eventually, the design will be published on the main minDUINO page under the Creative Commons Attribution Share Alike licence v4.0 for anyone to utilise as they see fit.