For a particular project Im working on we need a lot more analog inputs, on the order of 16 analog inputs while the Hydra only offers 6 analog inputs.
Doing some initial investigation Ive come across 2 main possibilities in terms of expanding the number of analog inputs.
- External off CPU A/D with data transferred via SPI, I2C etc.
- Multiplexer connected to one of the Hydra CPUs analog inputs, plus a number of digital pins on the Hydra to select the analog channels via the multiplexer.
Some differences between the 2 approaches I can think of:
In the off CPU case you could potentially get an A/D converter with higher resolution compared to the Hydras 10bit resolution.
A/D sampling rate
In the off CPU case you could potentially get an A/D converter with a much higher sampling rate compared to the sampling rate you can achieve with the Hydra.
For my particular project neither the A/D resolution or A/D sampling rates are that critical.
What is fairly important though is how close together the analog channels can be sampled. In the ideal world given what were measuring all the analog inputs would be sampled simultaneously.
Does anyone know what the minimum sampling time between analog channels would be on the Hydra using the multiplexer listed above or even just using the 6 built-in analog channels on the Hydra?
Are there any other obvious or not so obvious alternatives Ive missed?