On the Parino card are twelve relays and 5 opto isolated inputs. But on the card are 7 opto couplers. This
means we have some spare fuctionality.
When I designed the card, in 1994, I had two gates on the second ULN 2003 unused. And wasting has always been
a shame, so these needed to be brought to active service. So I thought of two extra opto couplers that would
provide two open collector outputs which are run in parallel to the relays B and C.
And that's why the jumpers are between the relays and the ULN drivers. If you're going to use the open
collector outputs a lot, you can disable the involved relays by removing the jumpers.
I could now say that I designed the card such that two opto coupled inputs and the two open collector outputs
would come out in the same 8 pin PCB terminalblock, but that would have been a lie. But later, when I got
'into' I2C, it was a gift from the Gods. The fourth 8 pin terminal block was then called the 'Feature
connector' and it could be turned into a full I2C interface for the Parinocard. The interface would be wired
as follows:
- OC 1: SDA to I2C system
- OC 2: SCL to I2C system
- IN 1: SDA from I2C system
- IN 2: INT from I2C system
and it would all line up perfectly well, as can be seen in the picture above left.
The picture is one of the first prototype. It features 8 copper pins that mate with the Parino card feature
connector. I made this one many many moons ago. I guess now is the time to revive the project and make it
ready for Linux and perhaps Windows 2000.
Around 2001, I got myself a set of Press-n-Peel foil for making PCB's at home. The PnP system is nice, but you
definitely need the original laminator. When using a clothes iron, the results are far from constant.
Anyway, I used the Press-n-Peel system to cover a piece of copperclad and etched the remaining copper away.
The drilling was a drama with a handheld drill. But finally I succeeded in making two good enough PCB's.
On the left, you see the connector that mates with the Parino feature connector. On the right, the terminal
block releases the I2C signals to the world.
As you can see in the circuit drawing below, the I2C signals are pulled up with a 4k7 resistor and then
brought out to the world on the 6 pin terminal block. All signals are buffered with a small PNP transistor to
drive a LED. Small lightshows are a feast to the eye and the make debugging a lot easier.
On the PCB is room for two IC's. One is a PCF 8574 I/O port and the other is a PCF 8593 ADC/DAC component.
These IC's are here only for the experimenter when debugging the card or for very small systems.
The circuit drawing is simple and easy. You can do a lot of things with this small add-on card:
- Understand I2C operations
- Develop or improve an I2C driver
- Run a small I2C system
- Use it to buffer a bigger i2C project
Suit yourself. Build it, use it and publish your results on the web.
What you see here is a special, one-off, Parino I2C extension. It mates with the fourth PCB terminal block and
produces a full I2C bus on the basis of the Parino hardware. This means: a fully decoupled I/O bus on the LPT
port.
This is an example how the Parino card can mate with an I2C card.
There will be solid strands of copper between the two PCB terminal blocks on each PCB.
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