ad7730 problem
Dear Friend
First, thank you very much for your post.
As a matter of fact, I've experienced most of these problems during the implementation of the AD7730. When compared with similar chips, this is a wonderful one; but some difficult to operate.
As you know, there are several considerations that must be taken into account especially with the AD7730. Both hardware & firmware are of great importance needing a lot of attention. I agree with the John Miles regarding the noise problem. This can be solved in several ways. Providing a good power supply design, you can use an adaptor, as I've done.
Since, there is no schema of your design; it's hard to make any guess without some more detail. But let me ask some questions may help hopefully.
1. Does the chip AD7730 work properly? As a result of your experiments it may be destroyed! Try a new one.
2. Does the microcontroller work properly? As you know, after several programming cycles, it's better to use a new micro.
3. If there's a serial interface with computer, are you using a ferrite bead-insulated cable (noise-free)?
4. Have you considered the settling times after the instructions within the code? This is a very slow chip, so you need to make enough delay time.
As an important tip, to increase the resolution, applying some statistical operations on the data like rolling or moving average would help. In this regard, I recommend you read the articles below:
http://www.analog.com/library/analogDialogue/archives/39-12/weigh_scale.html
**broken link removed**
Good luck,