This is a device tree overlay for the Texas Instruments ADS1015 A/D. Minimal changes would be required for it to work with other chips from the same family (ADS 1013/1115 etc).
Getting Started
First you need to install the device tree compiler (assuming you are using debian/raspbian):
apt-get install device-tree-compiler
Now compile the .dts:
dtc -@ -I dts -O dtb -o ads1015.dtbo ads1015.dts
Move the compiled overlay object to the raspberry pi's /boot/overlays
mv ads1015.dtb /boot/overlays
Add the following line to the pi's /boot/config.txt to load the overlay at boot:
dtoverlay=ads1015
Options
By default the overlay will only expose a single channel in differential mode (Pos A0, Neg A1). To expose other channels, change the channel configurations, change the sample rate or change the amplifier gain/scale you need to set some additional options in /boot/config.txt. All these lines must follow the "dtoverlay=ads1015" line in config.txt.
To set the i2c slave address specify the address you set with the addr pin. The default of 0x48 assumes the addr pin is pulled to ground.
| Addr Pin Connected To | Address |
|---|---|
| GND | 0x48 |
| VDD | 0x49 |
| SDA | 0x4A |
| SDL | 0x4B |
dtparam=addr=0x48
The ADS1015 supports 2 differential channels or 4 channels referenced to ground. You must ensure you enable and configure channels properly as misconfigured channels will have undefined/unexpected results.
To enable a channel add the following line to your /boot/config.txt after the "dtoverlay=ads1015" line:
dtparam=chX_enable=true
Where X is a channel letter from a to d. To enable channel B:
dtparam=chb_enable=true
After enabling a channel you must set the channel mode, use the following table (from the ADS1015 datasheet):
| chX_cfg | Input MUX Setting | Mode |
|---|---|---|
| 0 | A0 (Pos) and A1 (Neg) | Differential |
| 1 | A0 (Pos) and A3 (Neg) | Differential |
| 2 | A1 (Pos) and A3 (Neg) | Differential |
| 3 | A2 (Pos) and A3 (Neg) | Differential |
| 4 | A0 and GND | GND Ref |
| 5 | A1 and GND | GND Ref |
| 6 | A2 and GND | GND Ref |
| 7 | A3 and GND | GND Ref |
dtparam=chX_cfg=0
You can optionally set the gain of the PGA on the device.
| chX_gain | FS |
|---|---|
| 0 | 6.144V |
| 1 | 4.096V |
| 2 | 2.048V (default) |
| 3 | 1.024V |
| 4 | 0.512V |
| 5 | 0.256V |
| 6 | 0.256V |
| 7 | 0.256V |
dtparam=chX_gain=0
You can optionally set the sample rate of the device
| chX_datarate | Samples Per Sec |
|---|---|
| 0 | 128 |
| 1 | 250 |
| 2 | 490 |
| 3 | 920 |
| 4 | 1600 (default) |
| 5 | 2400 |
| 6 | 3300 |
| 7 | 3300 |
dtparam=chX_datarate=6
PS. Some markdown renderers don't support the tables...