Interest in AVR+MSP430 "general purpose" proto board?

While working on my next book, I've built a small general-purpose
prototyping board. This PCB is also intended to be useful for those
projects where someone says "please prototype this" and it requires a
micro that's only available in SMD.

Here are the schematic and component placement:

<http://www.larwe.com/temp/526-prelim-schematic.gif>
<http://www.larwe.com/temp/526-prelim-layout.gif>

The board is 5.1"x3.0", 0.062" FR4 with immersion tin (RoHS) finish, 2-
sided solder mask and component-side silkscreen. FR4 is *not*
guaranteed to survive Pb-free reflow profiles, and this board is not
checked against manufacturability design rules; it is strictly
intended for hand assembly only. Because of this, I have modified a
couple of the footprints to make hand-soldering easier (I'm thinking
particularly of the leadless accelerometer footprint).

The board includes footprints and interface circuitry for an SD/MMC
card slot in SPI mode, two Motorola pressure transducers, an ADXL322
2D accelerometer, an AVR ATmega48,mega88,mega168,mega8 or mega16 OR
ATmega32/64/128 chip (in TQFP), and either one or two MSP430F2013s (in
TSSOP; would also support other 20xx series parts since they have
basically the same pinout). Can be configured for a global Vcc=5V or
3V, has two RS232-level 3-wire serial ports, and offboard .100"
connections for all uncommitted I/O (as well as most of the onboard
signals). The AVR block has connections for ISP, debugWire and JTAG;
the MSP430s each have independent SBW debug connectors and watch
xtals. There is also a small, isolated area for a quad op-amp package
in SOIC, with appropriate component spaces and wiring around it to
configure each quarter as an inverting or non-inverting op-amp, with
an optional cap across the feedback resistor. The main reason I will
be using this space is impedance matching for external transducers to
the ADC channels.

Is anyone else interested in this board? I am planning to order 100
for myself, and if there is interest from others I will probably order
1K. I would likely be able to sell them for about $6.50 including
[U.S.] shipping.

Any suggestions on what you think is missing?

 

Yes, make it PLC8 compatible. We plan on making a cheaper version
without internal A2D (< $2), those with ratiometric compensations are
too expensive (> $5). Ours will be ADXL278 pin compatible. We are
also looking for PLC8 socket for it. Have you seen any, since you
must be working on something similar?

We don't really want the MSP, unless you can program it from the AVR.
We would prefer an ARM instead, and be programmable from the AVR.
One programmable micro is enough. We want:

AT90USB82 (Atmel) + LM3S828 (Lmi) + PCF8576D (Nxp)

 

PLC8? Never heard of it, and Google gives no result.

That is, however, a different product. I was looking more for
suggestions like "I could really use this board if you added an RS485
transceiver" or that ilk.

 

May be PLCC 8.

Three pins on the long sides and 1 on the short side.
Used by several Analog Devices and Memsic Chips.
A custom socket might be possible.

 

Since you asked, why not add a C8051F41x footprint, and cover
all the bases ?
That gives you 12 bit ADC, 12 bit DAC, 5V Vcc, and 50MHz speed,
and access to (very) low cost ICE tools.

-jg

 

Do you have a specific device in mind? I could shuffle stuff around
and make room without too much trouble.

 

I like the MSP, but the 2013 is a pretty weak variant. And everyone
already has one of those MSP USB dongle devices.

I concur with the other poster that Arms are great, but that goes
against the theme here. I think 8 and 16 bit processors are the focus
here.

LM324 Op-amps are bit dated by today's standards.

I'd go with a low-dropout regulator.

It's a pet peeve of mine to have SD slots if there's no SD filesystem
software. Of the hundreds of DEV boards that have a slot, only a
couple have open software to utilize the slot. I'm not sure if the AVR
world has this kind of open software?

I'd probably throw in an RTC and Termperature chip, both preferably
I2C.

 

C8051F410-GQ is the LQFP32 32KF
C8051F412-GQ is the LQFP32 16KF

These are normally ex stock at Digikey / Mouser.

-jg

 

Bear in mind that this board is (a) for building little customer
projects that I can't do on .100" perfboard, and (b) for my fourth
book, which is about the MSP430, inter alia. The ez430 is great, but
the target board in there has no footprints for, say, accelerometers.

Really, I put the MSP430 in the same general performance category as
the high end of 8 bits.

True, but the pinout is used by a lot of other quad op-amps. In fact,
I think the majority of quad op-amps in SOIC14 are pin-compatible.

Noted... however you probably also observed that a lot of the
components have no values. This is because they are TBD and
application-dependent. There are low-dropout versions of the LM317 in
the same SOT223 package, which the user is free to substitute
according to the application needs.

I can feel utterly insulated against this peeve, since I have
published a public domain FAT12/16/32 filesystem and have tested it on
AVR and MSP430, among other platforms
<http://www.zws.com/products/dosfs/index.html>
(Please note, there are a few bugs in the current version up there.
I'm working on updating the site).

Hmm, I'll look at that. Thanks for the feedback. In my application,
the temp sensors need to be attached to various mechanical hardware -
so they are wired to the I2C bus on flying leads.

 

Okay. I'll look at the eval board configuration and see if it will
fit.

 

The C8051F412, has both of these included. - 12 bit OnChip
Temp Sensor, and a 47 bit 32KHz Osc/Ctr/Alarm system, with battery backup.

-jg

 

In response to feedback, I'm making the following changes to the
board:

- Dimensions to change to approx 3.75 x 5.00". Size is designed to fit
Hammond Manufacturing p/n 1591ESBK polystyrene box (Digi-Key p/n HM106-
ND) with a small free space for batteries
- Add footprint for MCP9800A0 or MCP9800A5 -55 to +125C temperature
sensor on I2C bus
- Add footprint for ST M41T0 real-time clock IC on I2C bus. Separate
pads for attaching an external backup battery
- SD socket moved to overhang edge of board by ~80 mil in order to
protrude through edge of 1591ESBK box if desired.
- Remove DIP footprint for MSP430F20xx parts
- Add footprint for Cygnal C8051F410-GQ 32K flash fast low-power 8051
with 12-bit ADC, and associated debug connector
- Add pads for 0 ohm resistor to strap Vin+ to Vcc so the unit can be
run directly off a battery or externally regulated supply
- Add TPS60212 3.3V switcher to run the unit off one 1.5V cell if
desired (note: constraints apply)
- Wire accelerometer selftest line to AVR block
- Correct note in AVR block: ATmega32 is not supported

I expect I will have these in hand by May 14th or so.

 

Will you show this board on your web site before fab ?

donald

 

Yes, I'll show component placement and the actual copper - although
there will not be a whole lot of time to review it. I'll post a
notification here in c.a.e when it's ready. If you want an email
notification, send me an email (posting reply address is valid).

 

I suggest AT90USB1287 compatible. Only 7 pins needed for USB.

 

Okay, but I don't use that part, and both that part and the 64K
version are hard to get.

 

We can provide you with the chip for $10 each and your board for $2
each. We can also pre-mount the chip for you. I am heading to the
factory in a few weeks anyway.

 

Wow, that's cool!

I also like the C8051 devices from SiLabs that another poster has
talked about. I don't use the 8051 much, but SiLabs has some
compelling parts in that space. Their royalty-free USB and Ethernet
stacks are extremely good. SiLabs is also one of the best companies
when it comes to analog integration on their chips. They can do better
A/D than most others.

Maybe this isn't going to fit within the context of your book, but I
have recently become aware of an open source Java Virtual Machine for
Atmel AVRs. This is written in C (using gcc), and should be portable
to other processors also. The main requirement when porting it is to
provide native methods specific to the target device to provide
support for on-chip peripherals. The goal of this effort is
standardization at the software level to allow people to program all
kinds of devices in Java. Later, other source languages will target
the same virtual machine. Here's a link:
http://www.EricEngler.com/NanoVM.aspx

I also have a gcc IDE for Freescale 16 bit processors, and I'm
considering how best to move that effort forward. I'll likely port it
to .NET using my Pluto code base, where it will run on both linux and
Windows, and I'll integrate Java support also.
http://www.EricEngler.com/EmbeddedGNU.aspx
http://www.EricEngler.com/Pluto.aspx

By the way, I'm not advocating that you put a Freescale 16 bit
processor on your board because they no longer market this family to
the general purpose sector, even though it still has some compelling
features. Freescale now considers this to be an automotive family
almost exclusively.

Eric

 

*preen* It's quite satisfying indeed to have such an effective
rebuttal to a complaint!

I haven't used them in years, honestly, but adding the footprint costs
very little in terms of board space, given that I've made the area
larger anyway to fit that jiffy box.

No, it really doesn't. Though, it might make an interesting appendix.
My next book is about dimensioning your hardware choice for a desired
software goal, a task that most of the engineers I know don't do very
scientifically.

That is an interesting project, though - thanks for the link.

Oh dear me no, I don't do those any more. My last tangle with Motorola
[not counting POWER architecture chips] was the 68000 in the Amiga .

 

... Probably because the software goal arrives in the form of some arm
waving from marketing!

Another suggestion, if you have room....

Since this is about hardware selection to match design goals, can you
add a CPLD footprint ?

These are usefull for pushing the peripheral space, or just more IO,
or higher drive....

I'd suggest an ATF1502BE from Atmel. Digikey part, JTAG ISP,
TQFP44 package + IDC10 JTAG header cost. Tools are small [<10MB] and free.

-jg