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Even easier I2C bus interface :-)
Posted by: Anonymous User ()
Date: January 05, 2008 03:54AM

I'm trying to program some 24Cxx chips. I built this circuit earlier:

http://www.hw-server.com/constrc/seep.html

But I couldn't get the software to work in Windows. So I see PonyProg, which works in Linux (home) and Windows (work), and I'm excited. The Easy interface looks good:

http://www.lancos.com/e2p/easyI2Cbus.gif

But why does it need transistors and external power supply when the other circuit doesn't? Can it be simplified even more?

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Re: Even easier I2C bus interface :-)
Posted by: lancos ()
Date: January 05, 2008 12:54PM

You can use a simplified version of SI-Prog:
http://www.lancos.com/e2p/siprog_base.png
connected to this:
http://www.lancos.com/siprogsch.html#i2cbusadapter

You can simplify the base board avoiding to mount all components in external power box and connect C3 with C12.
Furthermore do not mount R4, Z3, R3, R1 and Q1.

Don't replace LM2936 with LM7805.

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Re: Even easier I2C bus interface :-)
Posted by: Anonymous User ()
Date: January 07, 2008 02:54PM

lancos Wrote:
> You can use a simplified version of SI-Prog:
> http://www.lancos.com/e2p/siprog_base.png
> connected to this:
> http://www.lancos.com/siprogsch.html#i2cbusadapter

The other still looks simpler. :-) Just wondering about the need for transistors and an external supply.

> Don't replace LM2936 with LM7805.

Why not? Because of the drop-out? The serial port supplies more than 5 V (+0.6 V)?



Edited 2 time(s). Last edit at 01/07/2008 03:07PM by endolith.

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Re: Even easier I2C bus interface :-)
Posted by: Anonymous User ()
Date: January 07, 2008 08:16PM

When I press "Probe" in the interface setup, what exactly is it checking? Just that it can see the parallel port itself, or does it try to write to the transistors and see that the input lines change? It shouldn't have any problem seeing the parallel port in Windows XP, right?

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Re: Even easier I2C bus interface :-)
Posted by: lancos ()
Date: January 07, 2008 11:14PM

endolith Wrote:
-------------------------------------------------------
> lancos Wrote:
> > You can use a simplified version of SI-Prog:
> > http://www.lancos.com/e2p/siprog_base.png
> > connected to this:
> >
> http://www.lancos.com/siprogsch.html#i2cbusadapter
>
>
> The other still looks simpler. :-) Just
> wondering about the need for transistors and an
> external supply.

The I2CBus need preferably open collector driver, so the need for the transistor.
Especially the SDA data line need to be bi-directional.
The external supply is needed since the LPT port can't provide a stable 5V.
This circuit (with the transistor) may be used even for in-circuit programming.

>
> > Don't replace LM2936 with LM7805.
>
> Why not? Because of the drop-out? The serial
> port supplies more than 5 V (+0.6 V)?

It's a low dropout with a very low quiescent current.

> When I press "Probe" in the interface setup, what exactly is it checking?
> Just that it can see the parallel port itself, or does it try to write to the
> transistors and see that the input lines change?

In the case of EasyI2CBus interface it writes to data-out and read back data-in

> It shouldn't have any problem seeing the parallel port in Windows XP, right?

If the LPT port is a standard (on board) LPT port there should be no problem.



Edited 1 time(s). Last edit at 01/07/2008 11:21PM by lancos.

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Re: Even easier I2C bus interface :-)
Posted by: Anonymous User ()
Date: January 09, 2008 10:37PM

lancos Wrote:
-------------------------------------------------------
> The I2CBus need preferably open collector driver,
> so the need for the transistor.
> Especially the SDA data line need to be
> bi-directional.
> The external supply is needed since the LPT port
> can't provide a stable 5V.

I am happy that I was able to make this work with external supply, but is there a way to provide power from LPT port? External battery supply is inconvenient. It would be nice to just have a cable with a IC grabber at the end. Each pin of the LPT port can drive 2 mA or so, and the I2C EEPROMs only draw 3 mA during write, so if the program holds all the other data lines high, and they are connected with diodes (just in case) to make +V, there should be plenty of current available for these chips.

The only problem I see is that on my computer's parallel port, it looks like the output pins are +3.3 V, while the computer's internal pull-ups on the data lines are +5 V, so when these two transistors are open, the internal pull-up pulls the SDA and SCL lines above 3.3 V. These lines are not supposed to be higher than VCC + 0.5 V, so maybe this is a problem, though the pull-up resistors prevent much current from flowing.

> It's a low dropout with a very low quiescent
> current.

But you *could* replace it with 7805 if that's all you had, right? Just that the other chip is better.

> In the case of EasyI2CBus interface it writes to
> data-out and read back data-in

Is it just pulling up one pin and down the other and checking at 12/13 that the correct inputs are seen?

> If the LPT port is a standard (on board) LPT port
> there should be no problem.

I had to switch on "Enable legacy Plug and Play detection" to get it to work, but then it worked.

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Re: Even easier I2C bus interface :-)
Posted by: lancos ()
Date: January 11, 2008 02:21PM

endolith Wrote:
> The only problem I see is that on my computer's
> parallel port, it looks like the output pins are
> +3.3 V, while the computer's internal pull-ups on
> the data lines are +5 V, so when these two
> transistors are open, the internal pull-up pulls
> the SDA and SCL lines above 3.3 V. These lines
> are not supposed to be higher than VCC + 0.5 V, so
> maybe this is a problem, though the pull-up
> resistors prevent much current from flowing.

This circuit is supposed to work at 5V. If you need 3.3V you should probably use another circuit with level translator buffer between LPT port and transistors.

>
> > It's a low dropout with a very low quiescent
> > current.
>
> But you *could* replace it with 7805 if that's all
> you had, right? Just that the other chip is
> better.

No, 90% of the times 7805 doesn't work because it isn't low dropout and sink too much current from COM port and the voltage fall too low. So the rules are:
1) external, at least 7.5V and 100mA: use 7805 or lm2936-z5 (indifferent)
2) internal, use lm2936-z5

> > If the LPT port is a standard (on board) LPT
> port
> > there should be no problem.
>
> I had to switch on "Enable legacy Plug and Play
> detection" to get it to work, but then it worked.

Oh thanks, I didn't know that. I should add to FAQ

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Re: Even easier I2C bus interface :-)
Posted by: Anonymous User ()
Date: January 14, 2008 11:14PM

lancos Wrote:
> This circuit is supposed to work at 5V. If you
> need 3.3V you should probably use another circuit
> with level translator buffer between LPT port and
> transistors.

I don't need 3.3 V; it's just the voltage output by my data lines on a motherboard-embedded parallel port. I was hoping there was a way to power the circuit from the parallel port.

> 1) external, at least 7.5V and 100mA: use 7805 or
> lm2936-z5 (indifferent)

That's what I meant.

> 2) internal, use lm2936-z5

Right.

> Oh thanks, I didn't know that. I should add to FAQ

I think this is an alternative to the method of changing DLPORTIO.SYS driver in the FAQ. I think this might be better than that method, though I don't know if it works in every case.

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Re: Even easier I2C bus interface :-)
Posted by: MaxHill ()
Date: September 03, 2013 07:11PM

lancos Wrote:
-------------------------------------------------------
> You can use a simplified version of SI-Prog:
> http://www.lancos.com/e2p/siprog_base.png
> connected to this:
> http://www.lancos.com/siprogsch.html#i2cbusadapter
>
>
> You can simplify the base board avoiding to mount
> all components in external power box and connect
> C3 with C12.
> Furthermore do not mount R4, Z3, R3, R1 and Q1.
>
> Don't replace LM2936 with LM7805.

Can anyone help - I have built this simplified HW but cannot connect?
WinXP SP3 - should I configure ports somehow?

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