OSX Typ350 ADS1220 Universal-ADC Sensor - User Manual

Device Type: Typ350
Chip: Texas Instruments ADS1220 (24-Bit Sigma-Delta ADC)
Interface: SDI-12 V1.3
Version: V0.1/28.02.2026/JoEm
Info: Documentation generated with AutoDoc

0350_ANALOG_4to20mA_PCB

PCB V1.1 for 0/4-20 mA (other versions: PT100, bridge, ...)

1. Overview

The T350 ("OSX Typ350") is a highly precise, universal analog data acquisition node based on the ADS1220. It supports up to 8 physical measurement channels (operating modes), which are fixedly configured via the array ad_physkan[] in the firmware source.

Typical applications:

High-precision PT100 temperature measurement (–70 … +120 °C, accuracy < 0.05 °C)
0/4–20 mA current measurement
Bridge sensors (load/pressure cells)
(Solar) radiation sensors
General differential and single-ended voltage measurement

Hardware connection (SPI signals)

Signal	Pin	Color (Cable)	Direction at ADC
SCLK	IX_SCL	yellow	IN
DIN (MOSI)	IX_SDA	green	IN
DO / #DRDY	IX_X0	white	OUT
#DRDY	IX_X1	blue	OUT
#Vcc (Pwr)	IX_X2	–	LOW = ON

Note

The ADS1220 operates with #CS permanently pulled LOW (SPI Mode 1, CPOL=0, CPHA=1). After power off, IX_X2 pulls the SPI lines to GND via 2 × 15 kΩ resistors.

2. Physical Channels (`ad_physkan[]`)

The firmware knows 8 physical channels (indices 0–7). Each channel has a fixed configured operating mode (typ), ADS1220 register configuration, averaging, and unit.

2.1 Operating Modes (`typ`)

`typ`	Constant	Description
1	`P_TYP_ITEMP`	Internal chip temperature of the ADS1220
2	`P_TYP_PT100_A`	PT100 via 2 kΩ reference + IDAC 1 mA + polynomial linearization
3	`P_TYP_STD`	Standard ADC (single-ended or differential), result in mV or counts

2.2 Channel Overview

Idx	SDI-12 Cmd	Type	Configuration	SPS	Averaging	Calibration	Unit	Measurement Time
0	M2	1	Internal temperature	45	1×	no	`oC_int`	~22 ms
1	M3	2	PT100 (ext. reference, IDAC)	45	8×	yes	`oC_PT100`	~453 ms
2	M4	3	Single-Ended AIN0	45	4×	yes	`mV_S0`	~275 ms
3	M5	3	Single-Ended AIN1	45	4×	yes	`mV_S1`	~275 ms
4	M6	3	Single-Ended AIN2	45	4×	yes	`mV_S2`	~275 ms
5	M7	3	Single-Ended AIN3	45	4×	yes	`mV_S2`	~275 ms
6	M8	3	Differential AIN0–AIN1	45	8×	yes	`mV_D01`	~453 ms
7	M9	3	Differential AIN2–AIN3	45	8×	yes	`mV_D23`	~453 ms

Calibration (Cali-Flag): When active, an offset zero point is automatically determined and subtracted before the actual measurement by internally shorting the inputs (AIN_p/n to AVDD/2). This approximately doubles the measurement time.

2.3 Technical Details of Operating Modes

Type 1 – Internal Temperature (`oC_int`)

Uses the internal temperature sensor of the ADS1220
Resolution: raw value / 32768 = °C
Configuration: ITEMP_CONFIG = 0x5022E0
- TS_ENA (internal temperature sensor active), single-shot, external reference (irrelevant), FIR 50/60 Hz
Measurement time: approx. 22 ms (1 sample, no calibration)

Type 2 – PT100 (`oC_PT100`)

2-wire PT100 with 2 kΩ reference resistor and 1-mA IDAC
2nd degree polynomial linearization (coefficient-based, determined by calibration):

Note

Hardware must support PT100

T = c₀ + c₁ ⋅ x + c₂ ⋅ x²

with the linearization:

c₀ = −2.457390 × 10², c₁ = 7.022650 × 10⁻⁵, c₂ = 8.966090 × 10⁻¹³

Valid range: raw value 2,427,000 … 4,910,000 counts (approx. –70 … +120 °C)
Configuration: PT100_CONFIG = 0x80562406
- AIN0/AIN1, GAIN=8, PGA AN, EXT-REF, IDAC1 → AIN3, 1 mA
Measurement time: approx. 453 ms (8 samples, calibration active)

Caution

If the raw value is outside the valid range, the PT100 channel returns –99 °C (sensor break or range exceeded –70 … +120 °C).

Type 3 – Standard ADC (`mV_…`)

Single-Ended (SE): AIN0–AIN3 vs AGND, GAIN=1, PGA disabled
- Conversion factor: SE_MULTI_G1 = 2.4414e-4 (2.4414 × 10⁻⁴) → result in mV
- Internal reference (approx. 2.048 V → measurement range 0 … 2048 mV)
- Configuration SE0: SE_CONFIG = 0x102481
Differential (DE): AIN0–AIN1 or AIN2–AIN3, GAIN=128, PGA active
- Conversion factor: DE_MULTI_G128 = 1.907e-6 (1.907 × 10⁻⁶) → result in mV
- Internal reference → measurement range ±16 mV (with GAIN=128)
- Configuration DE01: DE_CONFIG = 0x10240E

Note

Hardware for 0/4–20 mA current measurement must include a 100 Ohm shunt resistor. For bridge measurement, the bridge should be set to a level of approx. 1 V, e.g., via a high-impedance voltage divider.

3. SDI-12 Standard Measurement Commands

Note

Measurement is performed with the standard SDI-12 commands aM!, aM1! … aM9! (and of course also combined with CRC: aMC!, aMC1! … aMC9!). Here only the commands M and later X and I are documented; all other commands correspond to SDI-12 standard V1.3 (see SDI-12 specification).

3.1 Command Overview

Command	Channels	Description
`aM!`	All active channels	Measures all channels whose bit in the `m0_mask` register is set
`aM1!`	All active + VSup	Like `M`, additionally supply voltage (`VSup`) as the last channel
`aM2!`	Channel 0 (internal temp)	Only internal chip temperature (`oC_int`)
`aM3!`	Channel 1 (PT100)	Only PT100 temperature (`oC_PT100`)
`aM4!`	Channel 2 (SE AIN0)	Only single-ended channel AIN0 (`mV_S0`)
`aM5!`	Channel 3 (SE AIN1)	Only single-ended channel AIN1 (`mV_S1`)
`aM6!`	Channel 4 (SE AIN2)	Only single-ended channel AIN2 (`mV_S2`)
`aM7!`	Channel 5 (SE AIN3)	Only single-ended channel AIN3 (`mV_S2`)
`aM8!`	Channel 6 (DE AIN0–AIN1)	Only differential AIN0–AIN1 (`mV_D01`)
`aM9!`	Channel 7 (DE AIN2–AIN3)	Only differential AIN2–AIN3 (`mV_D23`)

a = SDI-12 address of the sensor (default: 0)

Error values in measurement result:

Value	Meaning
`–99`	PT100: Outside measuring range / break
`–9998`	ADC initialization error
`–9999`	General measurement error

4. SDI-12 Advanced Commands (`X` commands)

All configuration commands start with aX followed by the command letter. For reading, no = sign is used, for writing use =Value. Each command ends with !.

Warning

All parameter changes are volatile (RAM). Only aXWrite! saves them permanently in Flash (NVM).

4.1 Coefficients (`K`) – Individual scaling per channel

Each physical channel has 2 coefficients: Multi (even index) and Offset (odd index).

Application order:

Result = (ADC raw value × channel multi) × Kn_Multi − Kn_Offset

Coefficient table:

No.	Name	Default
K0	Temp_int.Multi	1.0
K1	Temp_int.Offset	0.0
K2	Temp_PT100.Multi	1.0
K3	Temp_PT100.Offset	0.0
K4	SEnd_0.Multi	1.0
K5	SEnd_0.Offset	0.0
K6	SEnd_1.Multi	1.0
K7	SEnd_1.Offset	0.0
K8	SEnd_2.Multi	1.0
K9	SEnd_2.Offset	0.0
K10	SEnd_3.Multi	1.0
K11	SEnd_3.Offset	0.0
K12	Diff_01.Multi	1.0
K13	Diff_01.Offset	0.0
K14	Diff_23.Multi	1.0
K15	Diff_23.Offset	0.0

Syntax:

Command	Function	Example
`aXKn!`	Read coefficient n	`0XK2!`
`aXKn=Value!`	Set coefficient n	`0XK3=0.5!`

Response: aKn=Value (e.g., 0K3=0.500000)

4.2 Channel Mask (`B`) – Active channels for M / M1

The bitmask m0_mask (1 byte) controls which channels are measured with M and M1.
Bit 0 → Channel 0 (iTemp), Bit 1 → Channel 1 (PT100), ..., Bit 7 → Channel 7 (DE23).

Default value: m0_mask = 60 = 0b00111100 → Channels 2, 3, 4, 5 active (SE AIN0–AIN3)

60 = 4 + 8 + 16 + 32 = Bit 2 + Bit 3 + Bit 4 + Bit 5

Command	Function	Example
`aXB!`	Read current mask	`0XB!`
`aXB=Value!`	Set mask (1–255 decimal)	`0XB=60!` (only SE AIN0–AIN3)

Response: aB=Value (e.g., 0B=60)

Bit assignment of channels:

Bit	Bit Value	Channel	Description	Active with m0_mask=60?
0	1	0	Internal Temperature	no
1	2	1	PT100	no
2	4	2	SE AIN0 (mV_S0)	yes
3	8	3	SE AIN1 (mV_S1)	yes
4	16	4	SE AIN2 (mV_S2)	yes
5	32	5	SE AIN3 (mV_S2)	yes
6	64	6	Diff AIN0–AIN1	no
7	128	7	Diff AIN2–AIN3	no

Example: Enable all SE channels + PT100

0XB=62!        62 = 2+4+8+16+32 (PT100 + SE AIN0…AIN3)
0XWrite!

Channel active status and full k output → Section 5.1.

4.3 Individual Unit (`U`) – Override channel label

Each channel has a default unit from ad_physkan[] (e.g., oC_PT100). This can be overridden per channel (max. 8 characters). If empty string is used, the default unit is applied.

Command	Function	Example
`aXUn!`	Read unit of channel n	`0XU1!`
`aXUn=Text!`	Set unit of channel n	`0XU1=degC!`
`aXUn=!`	Reset unit of channel n	`0XU1=!`

Response: aUn='Text' (e.g., 0U1='degC')

4.4 Output Precision (`P`) – Decimal places

Sets the number of decimal places for the SDI-12 output (0–9).
Special values 7, 8, 9: standard format %+f (printf default).

Format codes:

P-value	Format	Example output
0	`%+.0f`	`+23`
1	`%+.1f`	`+23.4`
2	`%+.2f`	`+23.45`
3	`%+.3f`	`+23.450`
4–6	…	…
7–9	`%+f`	printf-default

Command	Function	Example
`aXPn!`	Read precision of channel n	`0XP1!`
`aXPn=Value!`	Set precision of channel n (0–9)	`0XP1=3!`

Response: aPn=Value (e.g., 0P1=3)

4.5 Save Parameters / Identify Sensor

Command	Function
`aXWrite!`	Save all parameters (SDI address, coefficients, mask, units, precision) permanently in flash
`aXSensor!`	Query sensor type → response: `aADS1220!`

Important

aXWrite! must be explicitly called after each configuration change – otherwise all changes are lost on the next restart.

5. Command Line Commands (TB-UART / Debug Terminal)

These commands are available via the serial debug interface (tb_tools UART).

5.1 Device Commands (`device_type_cmdline`)

Command	Function
`k`	Output all coefficients (K0–K15) with names, current value, unit, precision, and active status (ON/bit number)
`p`	(Reserved, no function)

Example output k (with m0_mask = 60 – only SE AIN0…AIN3 active):

>k
K0: 1.000000 Temp_int.Multi(f) (Def: 1.0) Unit:'oC_int' Prec:2 OFF(1)
K1: 0.000000 Temp_int.Offset(f) (Def: 0.0)
K2: 1.000000 Temp_PT100.Multi(f) (Def: 1.0) Unit:'oC_PT100' Prec:3 OFF(2)
K3: 0.000000 Temp_PT100.Offset(f) (Def: 0.0)
K4: 1.000000 SEnd_0.Multi(f) (Def: 1.0) Unit:'mV_S0' Prec:9 ON(4)*
K5: 0.000000 SEnd_0.Offset(f) (Def: 0.0)
K6: 1.000000 SEnd_1.Multi(f) (Def: 1.0) Unit:'mV_S1' Prec:9 ON(8)*
K7: 0.000000 SEnd_1.Offset(f) (Def: 0.0)
K8: 1.000000 SEnd_2.Multi(f) (Def: 1.0) Unit:'mV_S2' Prec:9 ON(16)*
K9: 0.000000 SEnd_2.Offset(f) (Def: 0.0)
K10: 1.000000 SEnd_3.Multi(f) (Def: 1.0) Unit:'mV_S2' Prec:9 ON(32)*
K11: 0.000000 SEnd_3.Offset(f) (Def: 0.0)
K12: 1.000000 Diff_01.Multi(f) (Def: 1.0) Unit:'mV_D01' Prec:9 OFF(64)
K13: 0.000000 Diff_01.Offset(f) (Def: 0.0)
K14: 1.000000 Diff_23.Multi(f) (Def: 1.0) Unit:'mV_D23' Prec:9 OFF(128)
K15: 0.000000 Diff_23.Offset(f) (Def: 0.0)
Bitmask Channels: 60

The column at the end of the line indicates:

ON(BitValue)* – Channel is active (bit in m0_mask set)
OFF(BitValue) – Channel is inactive (bit not set)
Only Multi coefficients (even index) show the status; Offset coefficients (odd index) have no status suffix.

5.2 Debug Commands (only if `#define DEBUG` is active)

Tip

Debug commands are only available if #define DEBUG is active in the firmware.

Command	Function
`a<n>`	Measure channel n (0–7) in continuous loop and output raw value, runtime and physical result. Exit with any key.

Example output a1 (PT100):

Val:1
AD-Reset: 0
Res:3456789 (P:470/Real:463 msec) => +21.456 oC_PT100
Res:3456901 (P:470/Real:461 msec) => +21.458 oC_PT100
...
AD-Deepsleep

6. Parameter Storage (NVM)

All changeable operating parameters are stored in the internal flash of the processor:

Parameter	Contents
`param.koeff[]`	16 float coefficients (K0–K15)
`param.m0_mask`	Channel mask for M / M1
`param.precision[]`	Output precision per channel (0–9)
`param.ind_unit[]`	Individual units per channel
`param.ble_advname`	BLE advertising name
SDI-12 address	Stored under `ID_INTMEM_SDIADR`

Storage is performed exclusively by aXWrite! (→ Section 4.5).

7. Device Identification

The sensor ID has the following format:

TT_A24_A_0350_OSX<MAC_Low_HEX>

Example: TT_A24_A_0350_OSX1A2B3C4D

TT = TT (internal identifier)
A24 = Analog Sensor 24 Bit
A = Software identifier
0350 = Device type
OSX = OSX master platform
<MAC> = Lower 32 bits of the BLE MAC address (corresponds to standard BLE advertising name)

8. Factory Default Configuration

Parameter	Default value
SDI-12 address	`0`
m0_mask	`60` (channels 2–5 active: SE AIN0…AIN3)
Precision	K0:2, K1:3, K2–K7:9 (printf-default)
All coefficients	Multi=1.0, Offset=0.0
Individual units	empty (channel default)

9. Quick Reference SDI-12 Commands

aM!           Measure all active channels
aM1!          Measure all active channels + supply voltage
aM2! – aM9!   Measure single channel 0–7
aXKn!         Read coefficient n
aXKn=val!     Set coefficient n
aXB!          Read channel mask
aXB=val!      Set channel mask (e.g., 60 = only SE AIN0…AIN3)
aXUn!         Read channel n unit
aXUn=str!     Set channel n unit
aXPn!         Read channel n precision
aXPn=val!     Set channel n precision (0–9)
aXWrite!      Save parameters in flash
aXSensor!     Query sensor type

OSX Typ350 ADS1220 Universal-ADC Sensor - User Manual

1. Overview

Hardware connection (SPI signals)

2. Physical Channels (ad_physkan[])

2.1 Operating Modes (typ)

2.2 Channel Overview

2.3 Technical Details of Operating Modes

Type 1 – Internal Temperature (oC_int)

Type 2 – PT100 (oC_PT100)

Type 3 – Standard ADC (mV_…)

3. SDI-12 Standard Measurement Commands

3.1 Command Overview

4. SDI-12 Advanced Commands (X commands)

4.1 Coefficients (K) – Individual scaling per channel

4.2 Channel Mask (B) – Active channels for M / M1

4.3 Individual Unit (U) – Override channel label

4.4 Output Precision (P) – Decimal places

4.5 Save Parameters / Identify Sensor

5. Command Line Commands (TB-UART / Debug Terminal)

5.1 Device Commands (device_type_cmdline)

5.2 Debug Commands (only if #define DEBUG is active)

6. Parameter Storage (NVM)

7. Device Identification

8. Factory Default Configuration

9. Quick Reference SDI-12 Commands

2. Physical Channels (`ad_physkan[]`)

2.1 Operating Modes (`typ`)

Type 1 – Internal Temperature (`oC_int`)

Type 2 – PT100 (`oC_PT100`)

Type 3 – Standard ADC (`mV_…`)

4. SDI-12 Advanced Commands (`X` commands)

4.1 Coefficients (`K`) – Individual scaling per channel

4.2 Channel Mask (`B`) – Active channels for M / M1

4.3 Individual Unit (`U`) – Override channel label

4.4 Output Precision (`P`) – Decimal places

5.1 Device Commands (`device_type_cmdline`)

5.2 Debug Commands (only if `#define DEBUG` is active)