Sinclai ZX computers (ZX81/Spectrum) don't ship with a joystick port but they can count on the ubiquitous Kempston interface to provide 4 directional lines plus 3 buttons and that is more than enough to connect a Sega Master System HPD-200 paddle controller.

Paddle detection and reading code provided by SMS POWER. I/O address changed to match Kempston (0x1F), though.

A simple hardware adapter is necessary in between the Kempston interface and the HPD-200 paddle

An alternative for the HPD-200 is to build a DIY SMS/MarkIII paddle controller by Raphaël Assénat. In such case the wiring can be modified to route the  signals from  pins 5,7 and 9 thus dispensing the use of the adapter.

Example code (work still in progress) available at my github repository.

PCB for ZX97 lite on a CP200s case. Kicad files available at github

I believe it is possible to add a backporch for ZX97 (original) using three available gates from U25.

D11 discharges the capacitor at each negative horizontal pulse coming from /CSYNC and causes pin 11 of IC25 to go LOW, which blanks the video output signal at U25C.

After the sync pulse leaves R4 start to charge the capacitor. While the voltage is below positive threshold of U25 inputs the video stays blank, thus generating the backporch level. After that the output of U25D goes HIGH and the video content coming from U5B pin 8 can reach the output.

It might be necessary to fiddle with the value of R24 according with the technology of U25 (LS, HC, HCT, etc)

The resistors R1,R2,R3 were calculated to provide full compatibility with RS170: 1Vpp @ 75 Ohms load, 70% Video, 30% sync, DC coupling at output (the latter is a de facto standard). 

This circuit have not been tested yet on the ZX97 but works like a charm on TK85 (a ZX81 clone)

One of the users at msx.org tech forums asked if was possible to use Atari 7800 joypads in MSX.

The 7800 controllers are very similar to 2600 and therefore to MSX. The main difference is that to maintain compatibility with 2600 joysticks whilst providing two buttons, the 7800 used active high buttons on pins 5 and 9 which are used in 2600 for paddle inputs.

The straightforward solution is to invert the signals and that can be accomplished by a pair of NPN transistors.

Controller and adapter schematics, side by side, for better understanding.

PCB for prototyping retro computing and gaming projects.

100 mils spacing up to 72 vias edge connector, 36x28 (1008) vias prototyping area.

Available for download or order at oshpark

My version of PCB for "SD2IEC Revisited" from Retrohax (https://www.retrohax.net/sd2iec-revisited/). 
Hand routed, has basically the same dimensions and can be even built by tone transfer (no vias under components).

Board shared at OSHPARK (link) and at Github (link)

My collection of homemade projects stuffed inside Tic Tac boxes.

Bottle Openers

Built during a sunday morning out of scrap wood worked with files and sandpaper then finished using wood finishing oil.

Inspired by #Linear RGB LED Clockby Jan I decided to build my version. Instead of RGB LED addressable strip I'll be using regular LEDs and shift registers.

As I am planning to use the cheap chinese Digispark boards and a minimal of components. Since RESET pin is not available as I/O in most of the cheap boards I have only 5 pins to spare.

Two pins are for I2C communication with the RTC module

One pin will drive the shift registers using Roman Black's 1 bit shift system

The last two pins will be shared by a button and an LED each. Thus I need only three 8 bit shift registers (74HC595) for driving the remaining 24 LEDs

here's the draft for the circuit.

Browsing had.io pages I've stepped on the amazing #Zorkduino project wich implements a Z-Machine to play text adventure games (like Zork!).

The original project is very cool but it was build upon some ready made modules and a proto-board, so I've decided to route an specific board for the project named ZorkShield.

The board was designed to allow the assembly of both SD or MicroSD card slots and also allow the assembly of either a P2 stereo jack or a dual stacked RCA female for audio and video.

The video output have been slightly modified so the voltage and output impedance follow the RS-170 standard (like #VGA Blinking Lights). As a late time improvement I've added a RESET button.

Despite the board is a double layer It can be etched at home using tone transfer.

The layout was uploaded to OSHPARK but soon I'll upload it to github.

Today I have received a Microchip news with AVRs on it. That's the first time I ever seen Microchip advertising AVR microcontrollers. Despite the acquisition of ATMEL by Microchip is old news now this ad still blows my mind, lol!!!

After reading this post from @Radomir Dopieralski I couldn't help the challenge and completed the single sided version of the #Servo Breakout for WeMos D1 Mini board.

UPDATE: 3V/5V selection

Now I was able to Nyan!! I have used a 32 Ohm loudspeaker in series with a 220uF capacitor instead of the piezo buzzer.

It was necessary to put a 100nf between the VCC and GND of the microprocessor, otherwise it runs erratically.

Thanks again @Radomir Dopieralski for the board and for the code.

Finally found some spare time to assemble one of the #Nyan Boards that were kindly sent to me by @Radomir Dopieralski.

The rainbow colors match the original Nyan cat (from red to violet) and I have added a wire for the RESET signal.

Arduino support for Tone does not seem to work on Attiny85, so I am looking for an alternative way to play the sound.

Never gonna give up! Lol!!!!

Just finished the assembly of the Retro PC casemod.

Some details can be seen in my blog but here is another video slideshow for the impatient.

Based on Dynavision Radical, a Brazilian NES clone manufactured by Dynacom.

Specs:

• Motherboard BAT-TI2 with Celeron J1800 built in
• 8GB DDR3
• 120GB SSD
• Running Xubuntu 16.04 LTS
• Dual Genesis 6 button adapter powered by #AVeRCADE

Still in progress...

Composite video standard defines a signal with 1Vpp amplitude under a 75 Ohms. From that signal 70% (0.7V) is the amplitude of video information which stands above a 0.3V pedestal, while the synchronism information (sync tip) corresponds to the remaining 30% of the total amplitude or 0.3Volts below the pedestal.

Many projects of video generation for microcontrollers provide video signals that may work but don't respect the video standard, thus the signal generated might not be properly displayed depending upon the monitor used.

But generating a video signal with correct amplitude and impedance can be easily accomplished with the aid of resistors and some math.

Consider the circuit topology below where pin named VBIAS generates Sync signals, while VCOLOR pin generates video signals.

With two pins for generating the Sync and Video information we can have four possible combinations from which only three are expected: Sync level, Black (pedestal) and White Level.

We need then to calculate the value of the resistors wich can provide the following voltages

Black Level    0.3 Volt @ 75 Ohms
White Level    1.0 Volt @ 75 Ohms
Sync Level       0 Volt @ 75 Ohms

First thing to consider are the Voh and Vol from the microcontroller. Taking a PIC16F688 as example such levels can be in the range from VDD-0.7Volts to Voh and 0.6Volts to Vol. It means that our Sync level might be slightly biased to 0,3Volts under 75 Ohms load (0.6Volts without load).

Our amplitudes must then be corrected to compensate for the biased Sync level while maintaining the total amplitude in 1Vpp

Black Level	0.6 Volt @ 75 Ohms
White Level	1.3 Volt @ 75 Ohms
Sync Level      0.3 Volt @ 75 Ohms

Considering the resulting internal impedance of 75 ohms such values shall be doubled when no load is present.

Level   VSync  Vvideo  Vout(@75R)  Vout(no load)
Black   4,7V   0,6V    0,6V        1,2V
White   4,7V   4,7V    1,3V        2,6V
Sync    0,6V   0,6V    0,3V        0,6V

Now we have the necessary information to calculate the resistors. Let us use Kirchoff's current law: “At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node”

Then we have

Considering the voltages involved we have now the generic circuit equation:

Let us use Conductance instead of Resistance to make the math easier to deal with

Then for RL=75Ohms, VOL=0,6Volts e VOH=4,7Volts (PIC Vdd @ 5,4Volts) the equation for the three possible video levels are:

On the absence of load, RL = infinity, which means the Conductance is zero. Then we have the equations for the unloaded circuit.

The 6 equations can be written as a product of matrices

Using Scilab we can easilly get the resulting conductances.

>A=A={4.1 0 -0.6 ; 3.4 3.4 -1.3 ; 0.3 0.3 -0.3 ; 3.5 -0.6 -1.2 ; 2.1 2.1 -2.6 ; 0 0 -0.6}
>b=[ 0.6/75 ; 1.3/75 ; 0.3/75 ; 0 ; 0 ; 0 ]
>x=A\b

Which can be converted to resistances, resulting in

>x.^-1

Then using the most close commercial values we have:

Let's now do the oposite way and check which are the theoretical values we can achieve using commercial value resistors. Rewriting the equations in terms of Vout we have:

Then solving for the possible output levels we have:

Level   Vsync  Vvideo  V Out(@75R)  V Out (no load)
Black    4,7    0,6       0,64         1,29
White    4,7    4,7       1,35         2,71
Sync     0,6    0,6       0,17         0,35

output impedance by the ratio of voltages with and without the 75

Ohms load.

Vopen/Vload = 2,71/1,35 = 2,01

Then from Thèvenin:

In plain numbers we have ri=75 * (1,01) = 75,75 Ohms. Good enough!

The figure below shows the circuit with final values.

For calculating the resistor values for other microcontrollers and logic gates (TTL, CMOS) it is possible to use the general matrix system below. The green lines correspond to the voltage levels with 75Ohms load while the blue lines are the voltages with open circuit (no load).

Notes:

It is necessary to notice that the pins that drive the resistor must me able to source and sink currents around 25mA, which many microcontrollers can handle. On devices with...

I've been porting this the project #Shorty - short circuit finder form @jaromir.sukuba to the ATTiny45/85.

I have been working too on a single sided board for the project. The board takes 3.3" x 0.6" (roughly 84mm x 16mm).

Following a suggestion from [tekkieneet] to rotate the microcontroller 90 degrees and move the push-button to the right edge of the board I have redesigned the layout this time also using Kicad.

Here are the results

In Eagle

And in Kicad (dimensions in inches only)

I've posted a remark on the article "Creating a PCB in Everything" endorsing the design of single sided PCBs for DIY projects since they are far easier to replicate at home using techniques like toner transfer.

I've then started from original Nanite board and designed a single sided board for it, tinier as possible, using only PTH components.