microcontroller with built-in op-amp

address is fake.)

There are a few but performance is usually somewhat compromised compared to an external amp.

Some of the micros with delta-sigma ADCs have PGAs built in that would be suitable for that sort of application.

Best regards, Spehro Pefhany

--
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Check out Cypress' PSOCs. They have field-programmalbe analog gate arrays with zippy little MCU attached.

Noel

Hi Robert, look at

for the MSP430 series, there are devices with opamp, for example the MSP430FG437.

Andreas

You can also do this using a DAC, and an increasing number of mixed signal uC now also nclude DACS - see MSC12xx from TI, most SiLabs C8051Fxx series, some Philips LPC series (etc).

-jg

Not a great idea to amplify such a low level signal inside a micro banging the rails with digital noise. Your signal to noise ratio will be huge.

You are better off amplifying with an external op amp, with a good board layout to minimize noise floor. Then feed that into a micro with A2D inputs.

The PSoC fits the bill. BUT the Op-Amps and the analog have limitations. It may or may not work in your application.

The Zippy little MCU is limited by the weak C compiler. ( code is a little big and the ROM is a little small) (I am told ASM is OK) No bit operands. the Development environment has a big learning curve.

It is good for many things, But not all.

address is fake.)

A microcontroller on a chip is a too noisy friend to low-level analog signals, like strain gages.

Could you think the other way around: take an external very good A/D and use it on the bridge directly?

For examples, get Linear Technology LTC2420 data sheets and application notes.

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Tauno Voipio
tauno voipio (at) iki fi

Take a look at the UTI (Universal Transducer Interface) from Smartec

This interface almost any type of sensor (bridge, resistive, capacitive) to a uC. It compensates offset errors and the signal to the uC is a multi-phase squareware which contains the measured value as well as the reference value. Extremely good circuit. It is also used to measue fF capacities in Tunneling Electron Microscopes.

Meindert

Thanks to all of you for your very thoughtful comments and suggestions. Now I must digest it all to see what it means for my application, which is a body-mounted humidity logger for a medical research project.

-Robert Scott Ypsilanti, Michigan (Reply through this forum, not by direct e-mail to me, as automatic reply address is fake.)

True. But amazing things have been done with them.

I stick with assembly. I've been burned by c compilers in the past when code and data spaces are limited.

I agree.

Noel