How About An Ext Port Level Conversion/voltage Boost Kit?


urjaman

"I Know. We're going for a ride."
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Hello to all,

First i want to say that I'm just playing with the idea and I'm more like asking for this - essentially asking how many would like this and if somebody (maybe even OP?) would like to kit&sell or something.

So to the idea. The pandora has an EXT connector with 2 UARTS (if i remember correctly the 4-pin (with RTS/CTS) uart pins can also be used as GPIO, can the first too? (if so, 6 GPIO's)) with logic levels of 1.8V and a 2.8V 200 mA power supply. I'm assuming that a 3.3V or 5V supply and logic level conversion (to 3.3 or 5V) would be useful for a lot of people thinking of attaching their own electronics/µC's/whatever to the pandora.

So a simple chip list for my idea:
- 1*1.8V regulator
- 1*MAX756 3.3/5V boost converter
- 2*TXB0104 level converter
It would need some other stuff too, but skipping the listing for now (capacitors, diode, etc)
It's a bit sub-optimal to have 2 TXB0104's for 6 I/O lines (they provide 2*4=8), so if anyone has a better idea, just tell.

So, essentially these chips would be on a board that could be plugged to the pandora ext port (directly or via cable) and would have 8 (or more if we pass through the line in/out & tv-out?) pins of output:
GND, UART2 RX&TX, UART3 RX,TX,RTS,CTS, Vcc (3.3 or 5)

The MAX756 can easily be switched for 3.3V or 5V operation so it would be easy to configure for whatever device you want to attach. I've also crunced some current numbers for you. Given 80% efficiency (its upto 87%) the 5V output would have ~90mA. If set to 3.3V then you would have ~136 mA.

And yeah, one question for someone who knows the system, what happens if the 2.8V 200mA source is overloaded? Will it safely shutdown or will the entire pandora go down with it or what? Will it damage the device?
 
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Sounds interesting. If you posted the circuit diagrams for somthing like this, I'm sure a lot of people would use them.

QUOTE

And yeah, one question for someone who knows the system, what happens if the 2.8V 200mA source is overloaded? Will it safely shutdown or will the entire pandora go down with it or what? Will it damage the device?


Quite worrying. You're going to have to wait for MWeston to see the thread for an answer to that.
 
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'urjaman' said:
And yeah, one question for someone who knows the system, what happens if the 2.8V 200mA source is overloaded? Will it safely shutdown or will the entire pandora go down with it or what? Will it damage the device?
The EXT connector has VAUX3 all to itself. If you short it out, it can't take down the rest of the system unless the short results in thermal overload of the whole chip.

From the datasheet:
QUOTE
The short-circuit current for the LDOs and DC-DCs in TPS65950 is approximately twice the maximum load current. In certain cases when the output of the block is shorted to ground, the power dissipation can exceed the 1.2-W requirement if no action is taken. A short-circuit protection scheme is included in the TPS65950 to ensure that if the output of an LDO or DC-DC is short-circuited, then the power dissipation does not exceed the 1.2-W level.


Also, VAUX3 is supposed to be able to go to 3.0V according to the datasheet but I was told a long time ago that some voltages listed were not actually supported. I'm thinking that is old news now if they keep putting it in the datasheet. If it works (I've not tested it yet), a 3V setting will boost your efficiency overall (both in Pandora and boost converter).
 
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Okay, made some schematics for this. I'm also testing drop.io now - seems an ok place so see: CODE
http://drop.io/urjaman_
(I entered urjaman, then opened the howto link to a new tab, and somehow it had taken the name without ever asking me for password or recovery email (or any files), so thats why the _)

There's the eagle cad .sch and an exported .png (for you who only want to see the schematics fast). The schematic is based on ladyada's mintyboost v.1.1, so the license for this is creative commons attribution 2.5.

As a word of warning, i havent designed a board for this and the schematics are totally untested and with NO WARRANTY.

So, I'd like your feedback on this, if any.
 
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I'm no circuit designer, but looks like a real good idea for robotics etc.
I'd suggest adding the video out as well, its on the same connector, and may be useful for those doing external control stuff.
 
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What are the chances of it blowing up when plugged into a different voltage (think that's the right word) power source? (ie 110-220)?
 
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'Username' said:
What are the chances of it blowing up when plugged into a different voltage (think that's the right word) power source? (ie 110-220)?
The Pandora is always supplied by the same input voltage, if that's what you mean. A Pandora AC adapter would supply 5v (IIRC) whether plugged into 120 or 240.
 
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'Username' said:
What are the chances of it blowing up when plugged into a different voltage (think that's the right word) power source? (ie 110-220)?
Ugh, what(?!?)... there are no high voltages involved in my schematics. The voltage problem is solved already in the pandora's adapter (charger), which (i think) is an SMPS that can take 110-240 volts no problem.

The power source of my schematics is the pandoras EXT port which has 2.8V 200mA DC (some 0.56W of power).

EDIT: atomicthumbs beat me to it (GPRS fail...)
 
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'urjaman' said:
Okay, made some schematics for this. I'm also testing drop.io now - seems an ok place so see: CODE
http://drop.io/urjaman_
(I entered urjaman, then opened the howto link to a new tab, and somehow it had taken the name without ever asking me for password or recovery email (or any files), so thats why the _)

There's the eagle cad .sch and an exported .png (for you who only want to see the schematics fast). The schematic is based on ladyada's mintyboost v.1.1, so the license for this is creative commons attribution 2.5.

As a word of warning, i havent designed a board for this and the schematics are totally untested and with NO WARRANTY.

So, I'd like your feedback on this, if any.
Mmmmmm. Robot porn.
 
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'Butterman' said:
Mmmmmm. Robot porn.
I totally lol'd at this.

Anyways, I've worked a bit more on the schematic and even created a board just to see the size of the board needed. So again, see drop.io/urjaman_ . BTW, the board sizes in at 30.48x40.64mm - thats enough small for me :)
 
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'urjaman' said:
'Butterman' said:
Mmmmmm. Robot porn.
I totally lol'd at this.

Anyways, I've worked a bit more on the schematic and even created a board just to see the size of the board needed. So again, see drop.io/urjaman_ . BTW, the board sizes in at 30.48x40.64mm - thats enough small for me :)


Pics?
 
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'BackAssward' said:
'urjaman' said:
So again, see drop.io/urjaman_ .
Pics?

Okay, here we go with "direct" links,
Board image:
CODE

http://drop.io/urjaman_/asset/pandoraextboostr2brd-png


Schematic image:
CODE

http://drop.io/urjaman_/asset/pandoraextboostr2sch-png
 
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I would recomend that for this application you use 1 TXB0108 rather than 2 TXB0104's.
 
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'ashaw' said:
I would recomend that for this application you use 1 TXB0108 rather than 2 TXB0104's.
Oh, thanks (i never noticed that they had a 8-bit model).
More thanks if anyone can point out (/create?) an Eagle CAD part (.lbr) for the TXB0108PWR,
if nobody is interested, i will propably try to create it on my own, but I'm a noob with the library editor;
I did create the MSP1700 TO-92 part, but I'm not sure it's all correct... (And it was a tad simpler than the TXB's)
 
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I did up one for myself, it is not verry good I fear but it will do, see pdf at it.

CODE
http://alexisshaw.com/voltage_converter.pdf
 
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