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J

Joerg

Jan 1, 1970
0
Hello Folks,

As an analog guy I get goose pimples when I see converters like the
TLV1508. Impressive performance but, boy, do they need a complicated
liturgy to get data out of them. Many of them must be told via SPI that
I want to read this, that and the other value. Then you must patiently
wait x clock cycles, wasting away bus time. The guy who designs the host
processing will throw his coffee mug at me because there'll be a dozen
of these.

Here is what I am looking for: 10 bits or so, 8 channels, bone-simple
readout, can very very slow, low kHz range. All I need is to read DC
values and it doesn't matter when the exact sampling time was. SPI, I2C,
anything serial works. I mean, with a FIFO in there they should be able
to do continuous autoscan and just dump the last valid set of values
upon request.

Any ideas? I am also looking for 10-12 bit DAC with lots of channels but
that seems to be much simpler.

M

mkaras

Jan 1, 1970
0
Hello Folks,

As an analog guy I get goose pimples when I see converters like the
TLV1508. Impressive performance but, boy, do they need a complicated
liturgy to get data out of them. Many of them must be told via SPI that
I want to read this, that and the other value. Then you must patiently
wait x clock cycles, wasting away bus time. The guy who designs the host
processing will throw his coffee mug at me because there'll be a dozen
of these.

Here is what I am looking for: 10 bits or so, 8 channels, bone-simple
readout, can very very slow, low kHz range. All I need is to read DC
values and it doesn't matter when the exact sampling time was. SPI, I2C,
anything serial works. I mean, with a FIFO in there they should be able
to do continuous autoscan and just dump the last valid set of values
upon request.

Any ideas? I am also looking for 10-12 bit DAC with lots of channels but
that seems to be much simpler.

If you intend to interface into a microcontroller they why not design
in one of the microcontrollers that has 8 channels of A/D built in.
Very simple internal parallel interface. Examples are SiLabs C8051F126
with 8 channels of 12-bit A/D, Atmel ATMega16 with 8 channels of 10-
bit A/D or OnSemi MC68HC908GP32 with 8 channels of 8-bit A/D. Of
course there are many others.

- mkaras

R

Rene Tschaggelar

Jan 1, 1970
0
Joerg said:
Hello Folks,

As an analog guy I get goose pimples when I see converters like the
TLV1508. Impressive performance but, boy, do they need a complicated
liturgy to get data out of them. Many of them must be told via SPI that
I want to read this, that and the other value. Then you must patiently
wait x clock cycles, wasting away bus time. The guy who designs the host
processing will throw his coffee mug at me because there'll be a dozen
of these.

Here is what I am looking for: 10 bits or so, 8 channels, bone-simple
readout, can very very slow, low kHz range. All I need is to read DC
values and it doesn't matter when the exact sampling time was. SPI, I2C,
anything serial works. I mean, with a FIFO in there they should be able
to do continuous autoscan and just dump the last valid set of values
upon request.

Any ideas? I am also looking for 10-12 bit DAC with lots of channels but
that seems to be much simpler.

Joerg,
I'd employ a controller such as the AVR Tiny26 with 8
differential or 11 single ended 10 bit channels.
Since you need a dozend of them just hook them together
with an SPI or an USI.
Linear Tech has a a bunch of multichannel DACs with the
LTC2600 : 8x 12 bits for 9$as example. Rene J Joerg Jan 1, 1970 0 mkaras said: If you intend to interface into a microcontroller they why not design in one of the microcontrollers that has 8 channels of A/D built in. Very simple internal parallel interface. Examples are SiLabs C8051F126 with 8 channels of 12-bit A/D, Atmel ATMega16 with 8 channels of 10- bit A/D or OnSemi MC68HC908GP32 with 8 channels of 8-bit A/D. Of course there are many others. Unfortunately there isn't going to be a uC on those cards. Also, I found that many built-in converters are noisy no matter how clean the supply pins are kept. J Joerg Jan 1, 1970 0 Rene said: Joerg, I'd employ a controller such as the AVR Tiny26 with 8 differential or 11 single ended 10 bit channels. Since you need a dozend of them just hook them together with an SPI or an USI. I wanted to avoid a uC on there because it wouldn't be needed for any other purpose. They are too slow for the analog stuff I am doing on the boards. The ADCs on uC also tend to be noisier than stand-alone chips. Of course I could set up the uC to do autoscan and chips like the MSP430F2xxx have that feature in hardware. All you need to do is set one bit in a register upon initialize. Beats me why stand-alone ADCs don't have that. That way the host wouldn't have to talk, just enable CS via the correct address on the bus and then read the stream. Linear Tech has a a bunch of multichannel DACs with the LTC2600 : 8x 12 bits for 9$ as example.

Thanks, that could be a good one. I am currently leaning towards the
TLV56xx series. It all depends what's in stock because that is an
indicator of popularity, and sometimes of longevity as well.

L

linnix

Jan 1, 1970
0
I wanted to avoid a uC on there because it wouldn't be needed for any
other purpose.

Micros are sometimes cheaper than standalone ADCs.
You don't need to use them for anything else.
They are too slow for the analog stuff I am doing on the
boards.

How fast do you need?
Is 500KSPS too slow for you?
The ADCs on uC also tend to be noisier than stand-alone chips.

That's true. You have to be careful in layouts.
Of course I could set up the uC to do autoscan and chips like the
MSP430F2xxx have that feature in hardware.

Some have interval timer based conversions and auto averaging.

P

Peter Bennett

Jan 1, 1970
0
Hello Folks,

As an analog guy I get goose pimples when I see converters like the
TLV1508. Impressive performance but, boy, do they need a complicated
liturgy to get data out of them. Many of them must be told via SPI that
I want to read this, that and the other value. Then you must patiently
wait x clock cycles, wasting away bus time. The guy who designs the host
processing will throw his coffee mug at me because there'll be a dozen
of these.

Here is what I am looking for: 10 bits or so, 8 channels, bone-simple
readout, can very very slow, low kHz range. All I need is to read DC
values and it doesn't matter when the exact sampling time was. SPI, I2C,
anything serial works. I mean, with a FIFO in there they should be able
to do continuous autoscan and just dump the last valid set of values
upon request.

Max1202 - simple SPI interface and internal reference. No waits -
data comes out as you shift the command in.

--
Peter Bennett, VE7CEI Vancouver BC, Canada
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter

J

Joerg

Jan 1, 1970
0
linnix said:
Micros are sometimes cheaper than standalone ADCs.
You don't need to use them for anything else.

But they need to be flash programmed and are still more noisy.
How fast do you need?
Is 500KSPS too slow for you?

The ADC can be slow, a few kHz at the most. Not critical. What I meant
is that I can't use a uC for any of the control gear tasks. That would
have justified the hassle of in circuit programming. Unless you buy gang
programmers many manufacturers do not offer file dumps. They give you a
nice and cozy design environment but, for example, TI does not offer a
feature where you connect an EZ430 pod or the like and just download a
file right from the OS or from a web browser. You have to do that from
the IAR console. Not such a good thing in this case since the engineers
at my client are all specialized in optics and process control.
That's true. You have to be careful in layouts.

Even then they are noisier. Bond wires only provide so much in
conductivity and because form factor is a marketing concern they often
spring for a single VDD connection, two at the most.
Some have interval timer based conversions and auto averaging.

That would almost suffice. But chips like the MSP430F2012 even have a
nice SAR converter in there with autoscan. I still don't get why there
are no stand-alone converters with this autoscan feature. All the ones I
checked so far still needed an "invocation speech" to them via an SPI
write or were plain out of stock everywhere. The latter is a huge red flag.

J

Joerg

Jan 1, 1970
0
Peter said:
Max1202 - simple SPI interface and internal reference. No waits -
data comes out as you shift the command in.

Thanks. But according to its datasheet (page 11) you must still clock a
control byte into DIN. Seems just like all the others. Man, why do they
do this?

Also, that vendor isn't really my favorite. Got too many black eyes WRT
availability. Digikey only has 12 of these in SSOP, not a good sign and
not enough for even one unit in our case.

BTW, I clicked on their site for SSOP: Leadtime 16 wks. Ouch!

L

linnix

Jan 1, 1970
0
But they need to be flash programmed and are still more noisy.

The ADC can be slow, a few kHz at the most. Not critical. What I meant
is that I can't use a uC for any of the control gear tasks. That would
have justified the hassle of in circuit programming. Unless you buy gang
programmers many manufacturers do not offer file dumps. They give you a
nice and cozy design environment but, for example, TI does not offer a
feature where you connect an EZ430 pod or the like and just download a
file right from the OS or from a web browser. You have to do that from
the IAR console. Not such a good thing in this case since the engineers
at my client are all specialized in optics and process control.

Yes, I understand your concern. Programming environment is one reason
I am avoiding the MSP. At least with ARM, JTAG is possible. For our
particular project, we need to be able to JTAG one micro from another.

If flash is reliable, then I would not care about the programming
part.
I am not scared by the initial programming, but the possiblity of
re-programming in the field makes me nervous.

For example, flash is very likely the problem for the AT91Sam7S256
failing in the field. Failure is Failure, even if you can re-program
it.

J

Joerg

Jan 1, 1970
0
linnix said:
Yes, I understand your concern. Programming environment is one reason
I am avoiding the MSP. At least with ARM, JTAG is possible. For our
particular project, we need to be able to JTAG one micro from another.

I told them that, and certainly others did. All they'd have to do is
maybe hire an intern who can write a simple download routine so you can
dump data via SBW into the device without the design suite open.
Preferably without even needing to have a clue of what's happening. Just
by selecting a file, connecting the cable and hitting "Program Now".
It's not rocket science. But so far, nada.

The topper would be a wee sub-program that allows one-pin programming so
you could connect a little IR photodiode and then "beam it over". With
good encryption to avoid data errors in ambient light. Look, ma, no
cable! While it's no big deal to write such code for the MSP430 the PC
part would be a challenge, at least for an analog guy like me.

If flash is reliable, then I would not care about the programming
part.
I am not scared by the initial programming, but the possiblity of
re-programming in the field makes me nervous.

For example, flash is very likely the problem for the AT91Sam7S256
failing in the field. Failure is Failure, even if you can re-program
it.

Ouch, that would not be good.

L

linnix

Jan 1, 1970
0
I told them that, and certainly others did. All they'd have to do is
maybe hire an intern who can write a simple download routine so you can
dump data via SBW into the device without the design suite open.
Preferably without even needing to have a clue of what's happening. Just
by selecting a file, connecting the cable and hitting "Program Now".
It's not rocket science. But so far, nada.

But you are assuming that the bootloader is reliable, I would not rely
on that unless the bootloader is in hardware rom, not flash and not
eeprom.
The topper would be a wee sub-program that allows one-pin programming so
you could connect a little IR photodiode and then "beam it over". With
good encryption to avoid data errors in ambient light. Look, ma, no
cable! While it's no big deal to write such code for the MSP430 the PC
part would be a challenge, at least for an analog guy like me.

If the spec is open, someone would write it for you.
Problem is that most micro makers are protecting their programming

J

Joerg

Jan 1, 1970
0
linnix said:
But you are assuming that the bootloader is reliable, I would not rely
on that unless the bootloader is in hardware rom, not flash and not
eeprom.

The original one is hard-coded in but I don't remember whether that
ain't just a write-protected flash area.
If the spec is open, someone would write it for you.
Problem is that most micro makers are protecting their programming

Yep, and that is a rather silly business behavior. For TI it has already
cost them sales in my case. I had bugged them numerous times about some
more data about their MSP430 devices, then gave up on it. Went analog,
actually.

Just like a vendor who refused to disclose the schematic of a laser
controller, a schematic I only needed to find out what the plant
parameters would be. So, I designed it out. Slam bam, door shut. Even if
they came back now and repented it would be two days too late.

A

Jan 1, 1970
0
Joerg said:
Hello Folks,

As an analog guy I get goose pimples when I see converters like the
TLV1508. Impressive performance but, boy, do they need a complicated
liturgy to get data out of them. Many of them must be told via SPI that
I want to read this, that and the other value. Then you must patiently
wait x clock cycles, wasting away bus time. The guy who designs the host
processing will throw his coffee mug at me because there'll be a dozen
of these.

Here is what I am looking for: 10 bits or so, 8 channels, bone-simple
readout, can very very slow, low kHz range. All I need is to read DC
values and it doesn't matter when the exact sampling time was. SPI, I2C,
anything serial works. I mean, with a FIFO in there they should be able
to do continuous autoscan and just dump the last valid set of values
upon request.

Any ideas? I am also looking for 10-12 bit DAC with lots of channels but
that seems to be much simpler.
We use Texas TLV2543 a lot. 11 channels, 12 bit. Yes you need to send
a command to set up what channel you want to read, but the SPI gets the
result of the last conversion as you clock in the next command, so its
only one 16 bit transfer to read the last result and set the next one up.

--
Regards,

Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control

J

Joerg

Jan 1, 1970
0
We use Texas TLV2543 a lot. 11 channels, 12 bit. Yes you need to send
a command to set up what channel you want to read, but the SPI gets the
result of the last conversion as you clock in the next command, so its
only one 16 bit transfer to read the last result and set the next one up.

I can't use that one because the digital folks decided to go 3.3V. But
TI has similar ones that go down to 3V or even 2.7V. I guess I'll have
to use one of them, looks like no other choice.

Still I think it would be smart to market an SPI AD converter that has
it's own little clock, totally asynchronous from the SPI bus. Just a
simple RC or some cheap resonator. Then you could run that at a sample
rate that is low enough for part tolerance margins. Now, instead of
getting a first value that was acquired who knows when you could be sure
that it'll be rather recent, max x clock cycles ago. And it'll be there
almost instantly.

M

Marte Schwarz

Jan 1, 1970
0
Hi Jörg,
Even then they are noisier. Bond wires only provide so much in

I love the ADuC702x 12 bits resolution and not bad at all. Try it and love
it.

Marte

M

Marte Schwarz

Jan 1, 1970
0
Hi Jörg,
Still I think it would be smart to market an SPI AD converter that has
it's own little clock, totally asynchronous from the SPI bus. Just a
simple RC or some cheap resonator. Then you could run that at a sample
rate that is low enough for part tolerance margins. Now, instead of
getting a first value that was acquired who knows when you could be sure
that it'll be rather recent, max x clock cycles ago. And it'll be there
almost instantly.

again, why should a manufactor do this. Most people will use µC for this
operation. The Core for this is easy to write, every µC has RAM for a FIFO,
a Timer... and they are cheap...

Marte

J

Joerg

Jan 1, 1970
0
Marte said:
Hi Jörg,

I love the ADuC702x 12 bits resolution and not bad at all. Try it and love
it.

But then I have to learn a new uC ;-)

And around $8 for just the ADC function would be a hard pill to swallow. Plus when you look at Digikey stock is rather low for that series. I guess I'll go with one of those SPI varieties from TI. Don't know what National would have, can't see it after they managed to mangle up their web site. J Joerg Jan 1, 1970 0 Marte said: Hi Jörg, again, why should a manufactor do this. Most people will use µC for this operation. The Core for this is easy to write, every µC has RAM for a FIFO, a Timer... and they are cheap... Because I believe there is a market. Here's the current situation: There is a host system, a powerful computer. But the connection to the rack I am developing for this client will be via a USB bridge. Sure, we could add another layer of complexity by having a uC somewhere in between and I seriously thought about that. But if there was an auto-scan converter none of this is needed. Of course, then there is my favorite "fix" for situations like that: Build a poor-man's autoscan. Figure out what the ADC wants to hear, generate that somehow with a digital concoction and trigger this from ye olde 74HC4060. Works, done it before, has caused goose pimples in design reviews. Other scenario (that one is coming down the pike here soon): A mote. It only needs to measure one thing, once in a while, then send that info off to somewhere via a one-way serial link. Why should this need a uC and have to undergo all that costly EMC agency rigamaroo? M Marte Schwarz Jan 1, 1970 0 Hi Jörg, But then I have to learn a new uC ;-) I find it very easy to learn. With winarm package no additional cost, only$30 Minikit with serial download cable or simply samples, ready to start
with... Only the I2C I didn't understood clearly.
And around $8 for just the ADC function would be a hard pill to swallow. 7022 is with$4 delivering 10 AD ports with 12 bit.

the ADuC7022 may not be the cheapest solution, Atmel may have cheaper ones,
or Reneas, or...
The Analog MicroConverters do really have excelent AD-units. That's what I
know, this is what you didn't guess, me too, but we tested it.

Marte

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