smallest level converter solution?

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Hi - I like to have a serial connection on all of my AVR boards for debugging purposes. Thing is - I'm trying to cut down on space used on some of my boards - so I'm hoping to find a new solution for RS-232 level conversion. Right now I use MAX233s in SOIC packages (I can justify the extra cost as it saves a bit of space and everything I'm doing right now is 1 offs)

Anyways - I was looking at one of my AVRISPs and I noticed that there is no MAX232/233. As it turns out, it's done all with discrete components: http://www.atmel.com/dyn/resourc...

Alot of discrete components, in fact (14). I'm not sure if this results in less board space being used or a cheaper board or something else.

So - has anybody found a good solution for level shifting? I mean if I could just find a max233 in a qfn package I'd be happy...

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I don't know if the discrete solution is smaller/cheaper or not. Part of the reason for that level-shifting is that the ATAVRISPs work with RS232 levels on one side, and have an AVR inside that sends logic levels for ISP to an AVR on the other side that could be running at any Vcc from 1.7VDC to 5.5VDC.

You mean with all the empahsis on smaller devices like cell phones & PDAs that Maxim and National and TI have no RS232 tranceivers in tiny packages? And DigiKey & other big distis don't have any either? I'll have to fire up my search engines.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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DigiKey has two Maxims 10uMax that are 5mm x 3mm outside dimensions. There are also TSSOP packages listed at DigiKey; I believe those are smaller than SOIC.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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theusch wrote:
DigiKey has two Maxims 10uMax that are 5mm x 3mm outside dimensions. There are also TSSOP packages listed at DigiKey; I believe those are smaller than SOIC.

Lee


A search for max232 at digi-key only finds DIPs and SOICs. What search term did you use? Also - on Maxim's website they only list SOICs, DIPs, and LLCs.

edit: one solution I've been pondering is to just make a 3 pin connector that goes straight to ground, txd, and rxd on the avr. Then I'd make a cable with a built in level converter. I've seen devices powered off of the serial port - anybody know what pin I would use for power? But for some reason I don't like this solution.

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Quote:

A search for max232 at digi-key only finds DIPs and SOICs. What search term did you use?

Ummm--"MAX232" is one part number from a company called Maxim. And a MAX232 probably only comes in the packages found, but it certainly is possible that DigiKey does not carry or list all the available packages. You are looking for RS232 transceivers. Try searching for "rs232". And yes, they do list and have stock in several flavours of 10uMax.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Many of TI's RS-232 transceiver offerings are available in TSSOP, aren't they? That would be about a 5mm x 5mm package.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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theusch wrote:
Quote:

A search for max232 at digi-key only finds DIPs and SOICs. What search term did you use?

Ummm--"MAX232" is one part number from a company called Maxim. And a MAX232 probably only comes in the packages found, but it certainly is possible that DigiKey does not carry or list all the available packages. You are looking for RS232 transceivers. Try searching for "rs232". And yes, they do list and have stock in several flavours of 10uMax.

Lee

Now I am left wondering why max232s are used so often... The MAX3313E looks like a solid solution for me. It's in a 10 umax, 1 rx 1 tx, valid connection signal, 3 external caps, and half the price of a 232. Thanks.

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How bout the LT1381? nice and small

Imagecraft compiler user

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nleahcim wrote:
one solution I've been pondering is to just make a 3 pin connector that goes straight to ground, txd, and rxd on the avr. Then I'd make a cable with a built in level converter. I've seen devices powered off of the serial port - anybody know what pin I would use for power? But for some reason I don't like this solution.

That’s what we do for breadboard development.

But we use 4 pins and draw power from the breadboard for the RS232 transceiver.

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I've Used the ADM101E form Analog Devices
3x5mm package
Works great
3 external caps, 460kbps 1µA shutdown

Troy

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Maybe leave the connections to your device at avr levels and carry an "adaptor" that contains the level shifter.

---
Formerly Torby. Stitch626 just seemed a more descriptive nicname.

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Quote:

Maybe leave the connections to your device at avr levels and carry an "adaptor" that contains the level shifter.

Quote:

But we use 4 pins and draw power from the breadboard for the RS232 transceiver.

We've done a couple apps like that. Picture this: A Mega64 app, not all I/O pins used. 6-pin ISP header on the board, with Vcc, Gnd, RESET, SCK, PDI, & PDO. On the Mega64/128, PDI/PDO are aka RXD0/TXD0.

So we built a little adapter that plugs into the ISP header with serial transceiver circuitry. For RS232, we used a 9-pin shell with our ISP plug at one end and the circuitry inside the shell. Using the "spare" USART0 in this app, we now have an instant setup/monitoring/debugging/remote control port with $0 cost on the "production" boards.

This is kind of a luxury that doesn't show up in many apps. If we are applying a Mega162 or Mega64 we usually need both USARTs for the app.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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If you really want to go minimal, check out the 'RS232' level converters on the AVR Butterfly.

Smiley

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smileymicros wrote:
If you really want to go minimal, check out the 'RS232' level converters on the AVR Butterfly.

Smiley


It appears (http://www.atmel.com/dyn/resourc...) to be the same circuit as used on the AVRISP - 14 components by my count.

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Sorry, I didn't realize they were the same.

Smiley

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theusch wrote:
Quote:

Maybe leave the connections to your device at avr levels and carry an "adaptor" that contains the level shifter.

Quote:

But we use 4 pins and draw power from the breadboard for the RS232 transceiver.

We've done a couple apps like that. Picture this: A Mega64 app, not all I/O pins used. 6-pin ISP header on the board, with Vcc, Gnd, RESET, SCK, PDI, & PDO. On the Mega64/128, PDI/PDO are aka RXD0/TXD0.

So we built a little adapter that plugs into the ISP header with serial transceiver circuitry. For RS232, we used a 9-pin shell with our ISP plug at one end and the circuitry inside the shell. Using the "spare" USART0 in this app, we now have an instant setup/monitoring/debugging/remote control port with $0 cost on the "production" boards.

This is kind of a luxury that doesn't show up in many apps. If we are applying a Mega162 or Mega64 we usually need both USARTs for the app.

Lee


That's a nice solution - unfortunately it doesn't seem to be available on the chip that I am currently using - the 168.

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TroyC wrote:
I've Used the ADM101E form Analog Devices
3x5mm package
Works great
3 external caps, 460kbps 1µA shutdown

Troy


Looks identical to the MAX3311E - same features, same package even (though they give them different names - dimensions are almost identical)

A quick check at Digi-Key reveals no stock of it, but plenty of stock of the Maxim part though.

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sorry for bumping an old thread...

But in a new design I was planning on using a MAX3311E, when I suddenly realized it's designed for 5V systems. DOH.

Back to the drawing board...

So - does anybody know of a really small 1 rx 1 tx rs-232 level shifter for 3.3V systems? If it needs a 5V supply voltage (or greater) that's fine - but I don't want to use a 5V chip - as it'd mean another chip to buffer the signal, and that just goes against the whole idea of finding a really small chip. So far - the smallest I can find is a 16-TSSOP. Surely smaller chips are out there? So far I've checked Analog and Maxim, not sure who else makes small level converters.

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What is the problem with using an rs232 seperately between the boards and the computer?

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I use a simple circuit that requires 6 parts:
1 n-channel fet
1 npn transistor
3 resistors
1 diode

If you dont want to use the fet, use another npn
with a base resistor.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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Let me get this straight ... you are actually considering putting a MAX3223 or whatever on your board just for testing ? I wouldn't be allowed to do that in my company, your boss must be very lax.

When my products have no external comms interface (RS232, infra-red or whatever) I do however include 4 holes in a line 0.1" pitch (Vcc, GND, TX, RX) so I can connect via pogo pins on test or a molex for debugging to a separate "MAX232 Box"

Nigel

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Quote:
I wouldn't be allowed to do that in my company, your boss must be very lax.

Maybe he doesn't have a boss - I can't see any mention of one. On the other hand he does say he's doing mostly one-offs.
I get "extra hardware" tracked to facilitate development and debugging, you don't have to actually mount the components in the finished product, but then I have an extremely lax boss!.

Four legs good, two legs bad, three legs stable.

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John_A_Brown wrote:

I get "extra hardware" tracked to facilitate development and debugging, you don't have to actually mount the components in the finished product, but then I have an extremely lax boss!.

Yes I can get away with that ! In fact I even tracked in stuff on Project X that I knew I would need for project Y that I was due to start afterwards...Hey presto Project Y dev board already done.

Nigel

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nleahcim wrote:
So - does anybody know of a really small 1 rx 1 tx rs-232 level shifter for 3.3V systems? If it needs a 5V supply voltage (or greater) that's fine - but I don't want to use a 5V chip - as it'd mean another chip to buffer the signal, and that just goes against the whole idea of finding a really small chip. So far - the smallest I can find is a 16-TSSOP. Surely smaller chips are out there? So far I've checked Analog and Maxim, not sure who else makes small level converters.

Hmm.... A quick search of Maxim turned up the MAX3231E and the MAX3229E both in the UCSP 6x5mm package and both 3.3V capable from the quick spec sheet. Slap on four external caps and you're ready to rumble.
-Will

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outer_space wrote:
What is the problem with using an rs232 seperately between the boards and the computer?

http://www.sparkfun.com sells a couple of RS232 Shifter Boards. See this link for more information and schematics.

Don

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whein wrote:
nleahcim wrote:
So - does anybody know of a really small 1 rx 1 tx rs-232 level shifter for 3.3V systems? If it needs a 5V supply voltage (or greater) that's fine - but I don't want to use a 5V chip - as it'd mean another chip to buffer the signal, and that just goes against the whole idea of finding a really small chip. So far - the smallest I can find is a 16-TSSOP. Surely smaller chips are out there? So far I've checked Analog and Maxim, not sure who else makes small level converters.

Hmm.... A quick search of Maxim turned up the MAX3231E and the MAX3229E both in the UCSP 6x5mm package and both 3.3V capable from the quick spec sheet. Slap on four external caps and you're ready to rumble.
-Will

this is for a one off board - and I already have enough hard to solder chips on it... one DFN, probabaly soon two, and other nastiness... I'm not even sure I could hand solder a UCSP.

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N.Winterbottom wrote:
Let me get this straight ... you are actually considering putting a MAX3223 or whatever on your board just for testing ? I wouldn't be allowed to do that in my company, your boss must be very lax.

When my products have no external comms interface (RS232, infra-red or whatever) I do however include 4 holes in a line 0.1" pitch (Vcc, GND, TX, RX) so I can connect via pogo pins on test or a molex for debugging to a separate "MAX232 Box"

Nigel


This is for a one off university project :)

The 4 pin connector idea is starting to look more and more attractive to me - as I don't think I want to have a DB-9 connector on the board, so if I'm going to have a non standard connector anyways, why bother having the level shifter onboard? Yeah not sure myself. Sure wish DB-9s weren't such goliaths - on the last board I made that had a DB-9 the DB-9 + level shifter took up a good 30% of the board.

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donblake wrote:
outer_space wrote:
What is the problem with using an rs232 seperately between the boards and the computer?

http://www.sparkfun.com sells a couple of RS232 Shifter Boards. See this link for more information and schematics.

Don


Looking at their schematic they seem to have come up with a solution: http://www.sparkfun.com/datashee...

I don't see how that works though? What kind of IC is that?

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Quote:
I don't see how that works though? What kind of IC is that?

That is simply a dual "pre-biased" transistor package. A pair of general purpose
transistors combined with base resistors. You can just use common individual transistors
and duplicate the circuit. Theirs is a little cuter than mine, deriving a negative tx supply
voltage by "stealing" it from the rx line. You don't really need to do that because
most rs-232 receivers are really just npn transistors anyway, and a unipolar signal
drives them just fine.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma