Time for the µPF--2

 The µPF--2 

When I developed this µPF - 1 / B compatible board, I wanted from the start to add a specialized time management circuit. So I installed a DS3231. This circuit is interesting because it is very precise. It also offers RESET management that I used as a master reset of the board. 

This DS3231 operates using the I2C bus. Obviously, this bus must be implemented in the FPGA. That shouldn't be a problem. I thought I would find a usable 'piece of code' on the web. In fact it was not a good idea. The codes found are often complex and above all undocumented.

Therefore, the best solution was to implement the I2C protocol myself. That's what I did. It is not very complicated, but not necessarily straightforward.

After a short period of development, I got the bus to work perfectly and was able to configure and read this real time clock circuit:

At this point, I have tested all the hardware functionality of this project. I also rewrote a lot of the system. It only remains for me to integrate all these developments in a 'clean' way.

I am beginning to see the end of this subject ...

A SMALL MIDI TOOL!

 A few days after having ordered the realization of my printed circuit board, it has just arrived:

A very easy to assemble midi merge box

Unlike usual, I chose not to use SMD components but only through hole components. This will make it easier to assemble the circuit. I could even offer the circuit to be assembled as a kit if that interests some...

I am still waiting for the components, especially the switches and connectors, to carry out the first tests.

A SMALL MIDI TOOL!

A midi merge box

• Current synthesizers are now often equipped with software allowing their setting from a PC / MAC.
• For those who prefer hardware sound generators rather than software, the number of machines to be controlled tends to increase over the years.
• The topology of the MIDI network is not efficient when it is necessary to connect several MIDI out to a single MIDI in.
• Several solutions are available to overcome this problem but often it does not work well but still costs a 'certain' price.

In order to meet all these challenges, a few years ago I bought a USB / MIDI interface with 8 MIDI IN / OUT ports. Unfortunately, the management of MIDI information passing from external machines to the PC / MAC was buggy. Only 16 bytes were correctly treated. Longer messages were not transmitted correctly. Impossible then to download a complete set of patches.

Since I'm tired of buying unreliable devices, I decided to create my own very simple interface:

This interface is passive. That is to say that it does not control the MIDI packets arriving on the inputs to transmit them on the single output. 

This implies a single operating constraint: a single external device must send data at a given time to this interface. If the connected devices don't emit anything until you ask them to, that's okay. 

If a device continuously emits real-time information for example, and it is impossible to prevent it to do that, it is sufficient to easily disconnect it from the box, using the corresponding switch.

And the MIDI DIN5 sockets... I hate them. So I installed 3.5mm jacks for easier handling. It will obviously be necessary to make suitable cables but it is easy to do.

RETRO ][ : A Retro Apple 2

The adventure goes on. After having assembled an Omega MSX2 computer, an Easy Z80 under CP / M and a Maximite under Basic, this time I am attacking a clone of APPLE2, the RETRO] [ :

https://www.hackster.io/news/capture-apple-nostalgia-with-the-retro-computer-f0fc0ffda886

After starting by mounting the power supply, I actually noticed a problem with the two negative voltages of -12V and -5V. 

Both of these power supplies have a small design error. Nothing very bad but this implies on the one hand not to mount the two regulators concerned, as can be seen on the previous picture, and on the other hand to make the corrections to the printed circuit board.

This considered, nothing prevents continuing to build what will ultimately only be a prototype since a final version involves making corrections :

Nice board however!

New PSU for the PROPHET-VS

 The Sequential Circuits Prophet VS is a great synthesizer :

But it is also a machine that is not very well made. Poor quality components, perfectible printed circuits, spreading out of the processor buses inside the device, a PSU that heats up a lot, a very noisy transformer and above all a whole series of very poor quality connectors. Not to mention the 'famous' CEM5530 whose production at the time must be completely out of service today, reason why I had to develop a replacement clone years ago.

The copy I own has only really worked for a few years, after making a lot of changes. And yet, there would be more to do. And precisely, one of the really painful things in this machine, when it works and that one can use it, it is the very important noise which the power transformer generates: very boring.

So, I decided to replace the whole power system of this VS. There were several possible choices for creating a replacement PSU. I decided to create a generic power supply that can be used in other devices, and secure, without handling high voltages. 

I created a low voltage switching power supply with linear regulators on the + 12V and -12V outputs:

Beta version.

Output technical details:

• +5V     2A (switching)
• +12V   2A (switching + linear)
• -12V    2A (switching + linear)
• RESET signal
• /RESET signal
• +5V     BATTERY
• Power Error indicator
• Floppy type power connector

Input technical details:

• 2 x 18V/AC
• Thermal fuses

Advantages:

• Precise outputs
• Low heat dissipation in normal use

I have to admit that it took me several versions to sort out the little issues that I encountered and thus obtain a very reliable and convenient power supply. To install this new PSU, the first thing to do was to remove all the concerned components on the Prophet motherboard:

In my case, I also removed the memory backup battery because I equipped my Prophet with self-backed SRAMs. This avoids any possibility of problem due to a possible corrosion of the battery body which could cause serious damage to the printed circuit:

The components removed from the Prophet motherboard:

'Last' modification, I placed wires for + 5V, + 12V and -12V, intended to be connected to the new PSU:

After that, it only remained to place the new power supply into the Prophet, as well as the new transformer:

Regarding my VS, I saccrified the voltage selector and shortened it to be able to position the new PSU more easily. I obviously kept the fuse holder that I put in place of the voltage selector.

During my first operational tests, I observed some problems with the sound. The red LED on the PSU would light up at times, indicating a loss of regulation. It was normal since I did not have a 2x18V transformer available but only a 2x12V. The + 12V and -12V regulations could therefore not be provided correctly. 

So I ordered and received a few days later a German quality 2x18V transformer. In the meantime I also made the last modifications on the printed circuit of the PSU and mounted this new copy in the VS:

Self congratulation but... I am very satisfied with the result. The PSU works perfectly well. The error LED remains constantly off. The PSU heats up very moderately. Above all, the Prophet no longer emits any operating noise. And that is a real pleasure!

Exterior view:

Funny: the three green LEDs of the PSU illuminate the printed circuit board of the front face, which has the effect of nimbling the 'Enter' and 'Edit Waveform' switches with a green hallo.

If you are interested, this PSU is available. Contact me for more information:

Retro computing µPF--2, the first real start.

The implementation of the peripherals being different on this board, I had to modify the VHDL code of the system that was working on the generic FPGA board. It took me much less time than I expected to achieve a functional result:

For the moment I have only tested the displays. The next step will consist of checking the operation of the USB serial com port as well as the communication with the keyboard. But for now, the new µPF--2 board will be able to replace the generic FPGA board on my desk and it feels good because it's been a few months now since I started porting µPF--1 to an FPGA board:

OMEGA MSX COMPUTER : A USB keyboard converter

I am currently very busy developing the µPF--2 kit. However, I continue other development in parallel, including a USB keyboard converter for the MSX Omega computer:

More information here.