ADC

[oskaratk]

does Olimex have some kind of ADC that could be used with an A20?
If not, any recommendations? I need 2 analog inputs ...

Thanks
Oskar

[dave-at-axon]

What resolution do you need?

What voltage range input do you need?

The MOD-IO has ADC input but it means you have excess IO that you probably don't need.

I've just designed an ADC input board to connect to the UEXT connection and it communicates with I2C. 4 channels of 12,16 or 18 bit with 0-2.048V input. I use 4-20mA sensors so this range is ideal for my application. I use the Microchip MCP3428 for this.

Are you able to design make your own?

[oskaratk]

The MOD-IO would overkill and too expensive for my application

I guess, for a prototype I am going to use http://www.adafruit.com/products/1083#Description

In the long run, I may design ms own PCB. I need to monitor the charge state of a remote 24V battery (solar charged) system.

I need to measure the output of an ACS758 current sensor - which has an Vout of 0-5V and also the output of an voltage sensor .. Vout 0-5V as well.

Using a high resistance voltage divider would not be a problem .. so I could use the MCP3428

Also need 1 output to control a solid state relay, but the relay needs only 2.5V 7.5 mA to switch - I think that load a GPIO pin can handle directly

and yes, I can make/design solder my own PCB

Thanks
Oskar

[dave-at-axon]

Hi Oskar,

The own PCB idea is a good one. The DFRobot PCB service makes things like this cheap these days.

I've used the ACS758 into the MCP3428 before with a potential divider and it worked fine. I used the bi-directional version so I could measure charge and discharge current. Voltage was, as you said, a potential divider. Funnily enough, same application as yourself.

For the output and the cost of a single 2N2222A transisitor and a resistor I would use that to switch the solid state relay. You can also put a pull down on the input to the transistor to ensure the output is off during the boot cycle.

[oskaratk]

For the output and the cost of a single 2N2222A transisitor and a resistor I would use that to switch the solid state relay. You can also put a pull down on the input to the transistor to ensure the output is off during the boot cycle.

or go fancy and make it short-proof, use a SN754410 or such as "driver"