ADC
dev_sg features a 6 channel differential ADC with integrated programmable gain amplifier (PGA), with the following parameters:
| Analog sampling rate | 2kHz |
| Number differential channels | 6 |
| Number of bits | 24 |
| ADC reference voltage | 1.2V |
ADC operation
ADC values are sampled, and amplified via hardware PGA. The values are then normalised to the range [-1, 1], then an optional low pass filter may be applied. The ADC values are then passed through the transform subsystem, before being output as JCS signals.
ADC user configuration
Channel PGA gain
Select the ADC gain for channel X by writing an enum to adc_channel_X_gain (where X is 0, 1, 2, 3, 4 or 5):
| Gain parameter | Description |
|---|---|
ads131m06_gain_1 |
Gain: 1x (Default value) |
ads131m06_gain_2 |
Gain: 2x |
ads131m06_gain_4 |
Gain: 4x |
ads131m06_gain_8 |
Gain: 8x |
ads131m06_gain_16 |
Gain: 16x |
ads131m06_gain_32 |
Gain: 32x |
ads131m06_gain_64 |
Gain: 64x |
ads131m06_gain_128 |
Gain: 128x |
WARNING:
When operating with channel gain settings at: 8, 16, 32, 64 or 128, the ADC input voltages must not exceed 1.5V.
Channel mux
Configure the ADC input multiplexer by writing an enum to adc_channel_X_mux (where X is 0, 1, 2, 3, 4 or 5):
| Mux parameter | Description |
|---|---|
ads131m06_mux_ainp_ainn |
\(Ain_p\) and \(Ain_n\) are connected to the external pins (Default value) |
ads131m06_mux_shorted |
\(Ain_p\) and \(Ain_n\) are shorted to ground |
ads131m06_mux_pos_dc_test |
Positive DC test signal of around \({2 \over 15} \times v_{ref} = {2 \over 15} \times 1.2V = 160mV\) |
ads131m06_mux_neg_dc_test |
Negative DC test signal of around \({2 \over 15} \times v_{ref} = {2 \over 15} \times 1.2V = 160mV\) |
Note:
The DC test signal scales with the selected gain. For example, gain = 1, test voltage = 160mV, gain = 2, test voltage = 80mV
WARNING:
The ADC channel and mux configuration values are only sampled at startup.
Any changes to the mux or channel configuration while JCS is running will have no effect.
To re-configure the mux or channel values, a jcs_host API call to stop, then start is required.
ADC filter
The normalised ADC values may be passed through a first order low pass filter (one per channel), before being passed to the transform subsystem. The filters are either enabled for all channels, or disabled for all channels.
Enable or disable the ADC filter by writing an enum to adc_filter:
| Filter mode | Description |
|---|---|
adc_filter_disabled |
ADC filters disabled for all channels. (Default value) |
adc_filter_enabled |
ADC filters enabled for all channels. |
Configure the ADC filter with:
| Commands | Type | Required | Description |
|---|---|---|---|
adc_filter_fc_hz |
float32 | Optional | Filter cutoff frequency. Default: 1kHz |