Super-simple Econet Clock design

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simoni
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Super-simple Econet Clock design

Postby simoni » Wed May 25, 2016 6:46 pm

I've just finished designing and building an Econet clock for my BBC model B, Master and Archimedes Econet network which I am currently putting together.

Since I didn't feel like spending 70 quid or so on a clock (and since my other hobby is embedded electronics) I designed a clock which is configurable (in fact far more configurable than the other solutions I found) and simplistic in the extreme... it requires a single 8-pin chip (ATtiny45) and can be built on a bit of stripboard for a tenner or so (less for me since I had bits lying around). I saw a lot of posts on the web saying that it wasn't possible using a small 8-bit microcontroller... but it is if you are willing to troll through the datasheets to find the right one ;)

If you're interested in building your own then I've shared all the design and code on my website. It's open-source and open-hardware so you are welcome to do whatever you like with it 8) Note, that you will need an AVR programmer; but you can use an Arduino board to do it if you don't have one.

Of course, I'd love to hear back from you if you decide to try it out since I've only tested it on my own network.

Here's a link to the project (the page includes a zip file of all the ATtiny firmware source-code).

http://www.waitingforfriday.com/index.php/Acorn_Econet_Clock

/Simon

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sorvad
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Re: Super-simple Econet Clock design

Postby sorvad » Wed May 25, 2016 7:18 pm

=D> Great work

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danielj
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Re: Super-simple Econet Clock design

Postby danielj » Wed May 25, 2016 7:52 pm

Love it! Thanks for posting :D =D>

d.

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leenew
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Re: Super-simple Econet Clock design

Postby leenew » Wed May 25, 2016 8:33 pm

Good Work!
Love the website too.

Lee.

dangardner
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Re: Super-simple Econet Clock design

Postby dangardner » Wed May 25, 2016 8:53 pm

Good job! I did something similar with an Atmega32U2 breakout board with my DIY Econet clock but I used an RS422 differential line driver. The differential PWM from the microcontroller is a really nice touch but I'm wondering whether it has enough power alone to drive a full-length network. Is there any reason why you didn't use a (non-differential) RS422 line driver in the design?

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simoni
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Re: Super-simple Econet Clock design

Postby simoni » Wed May 25, 2016 9:05 pm

Good question dangardner... Well, looking at the SN75159 datasheet the maximum output current that can be driven by a pin is 40mA (that's 40mA per pin). The ATtiny45-20PU is rated at 40mA per pin too with a maximum Vcc to GND draw of 200mA. Since I'm only using two pins, I'm way under the load spec of the chip and easily in-line with the 75159 (although, since the output is differential I would expect the overall draw to only be a little over 40mAs).

The later modules used an AM26LS30 which can do 60mA per pin on the output drivers; but at the cost of another IC I didn't think it was worth it since my primary aim was to make it as easy to build as possible (and as cheap as possible).

If you wanted to use a driver chip you could; just connect the driver chip to the OC1B port (ignoring the !OC1B output) and take the differential signal from the driver IC. Then you wouldn't need to change the firmware. Unless you have a very impressively long bus network though I don't think you'd see much advantage.

/Simon

P.S. Thanks for the kind comments!

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BeebMaster
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Re: Super-simple Econet Clock design

Postby BeebMaster » Thu May 26, 2016 7:09 pm

Great news!

More clocks = more Econets = more progress to Acorn world domination!

Code: Select all

Who are you?

>*I AM THE MASTER
CH."OBEY"

You will obey me!
You will obey me!
Image

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simoni
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Re: Super-simple Econet Clock design

Postby simoni » Sat Jun 18, 2016 4:04 pm

After gathering some feedback on the original clock, I've now made a revised version which is a little more complex, but allows you to choose your clock configuration from a DIP switch (as well as some other nice additional features).

The project write up is available here:

http://www.waitingforfriday.com/index.p ... t_Clock_V2

/Simon

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IanS
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Re: Super-simple Econet Clock design

Postby IanS » Fri Dec 23, 2016 1:44 pm

simoni wrote:After gathering some feedback on the original clock, I've now made a revised version which is a little more complex, but allows you to choose your clock configuration from a DIP switch (as well as some other nice additional features).

The project write up is available here:

http://www.waitingforfriday.com/index.p ... t_Clock_V2


Following on from this - viewtopic.php?f=3&t=12312

It looks like your clock is the wrong way round. I assume you can probably fix it in software though.

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IanS
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Re: Super-simple Econet Clock design

Postby IanS » Sun Jan 22, 2017 3:07 pm

So I built a new clock based on this design:-
IMG_20170122_144602198.jpg

It has USB power input, and the facility to add a "proper" line driver (just so I could do some comparison), power indicator, and data line biasing to avoid needing a teminator on small (and large it seems) networks.
So far it all seems good. Can't tell any difference between using the line driver and the CPU outputs, even with ~40M of ethernet cable.
It also has a "Phil Blundell" compatible rj-45 socket for extending the network to other sockets. I've been using these:- viewtopic.php?f=41&t=5594&p=157254#p157254

The line driver enable signal is using the spare switch position, so it's easy to change the switch and fit links for comparison.

Thanks for making the design available, and open.

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simoni
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Re: Super-simple Econet Clock design

Postby simoni » Sun Jan 22, 2017 3:51 pm

Thanks for making the design available, and open.


You are most welcome :)

I'll have to get around to correcting the source on my site (to swap the pins) - to much to do!

Nice looking board btw; I like the RJ45 idea.

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IanS
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Re: Super-simple Econet Clock design

Postby IanS » Sun Jan 22, 2017 4:14 pm

The output pins from the CPU go to opposite corners of the 4-pin header (P5), so I can easily swap the polarity, or disconnect entirely. And either output pin can feed the line driver.

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simoni
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Re: Super-simple Econet Clock design

Postby simoni » Sat Feb 11, 2017 1:59 pm

Just a note on this. I've finally found the time to fix the polarity issue (and correctly test it all on the oscilloscope). The updated version of the clock firmware is now on GitHub (no modification to the hardware design was required).

https://github.com/simoninns/EconetClock2

/Simon

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IanS
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Re: Super-simple Econet Clock design

Postby IanS » Mon Feb 13, 2017 9:46 pm

When we were running my clock PCB (using your ATTiny code) at the Abug meeting, the slowest speed was a bit fast for transferring large files. It's also a bit quick for the Atom. We ended up using my old clock which runs at about 160kHz.

I've since modified the code to have a 255(96), 196(64) and 180(48) period(mark) for the slowest settings.

I still aim to do some more testing, but I think some slower speeds would be a good idea. I did see a graph of speed setting against machine and cable length somewhere, but I can't find it again now (I think it was an SJ Research doc). It suggested 230kHz was the highest practical speed possible with a beeb.


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