IoT Teensy BBB Cape Reference

The IoT Teensy Cape combines the real-time capabilities of a Teensy 3.2 with that of a BeagleBone Black running Debian Linux. Two terminals on the cape provide connections to the Teensy and/or the BeagleBone Black through jumpers on the back of the cape. The tables below provide the specifics of the connections.

Top of Teensy Cape:

Bottom of Teensy Cape (Includes Jumper Positions):

Rectifying Circuits:

The cape also contains three rectifying circuits to facilitate current measurements. The input of each circuit is a J2 terminal position and the output is a Teensy analog input. The specifics of the connections are as follows (this information is also included in the tables below):
  • J2 terminal position 23 – Teensy pin 23 (analog 9)
  • J2 terminal position 22 – Teensy pin 22 (analog 8)
  • J2 terminal position 21 – Teensy pin 21 (analog 7)

The rectifying circuit converts a 60-hertz sine wave shown in Figure 3 to a rectified wave shown in Figure 4. The rectified wave is always positive or zero voltage so analog-to-digital (ADC) converters can digitize the signal.

Communicating between the Teensy and the BeagleBone Black:
Typically, the Teensy will collect real-time data and then send the data to the BBB via serial communication for further processing and transmission. The serial communication is accomplished through UART1 of the Teensy and UART1 of the BBB. The cape contains connections between the pins on the Teensy and the BBB to accomplish the communication. No jumpers or external wiring is needed.
The pins are connected as follows (this information is also included in the tables below):
  • Teensy Pin 0 UART1 RX1 is connected to BBB P9_24 UART1 TX1.
  • Teensy Pin 1 UART1 TX1 is connected to BBB P9_26 UART1 RX1.

In order for the BBB to accomplish serial communication over UART, pins P9_24 and P2_26 must be configured. Instructions for doing so can be found here.

Cape Connection Mappings:

The following tables indicate how connections are made from the screw terminals to the Teensy and the BBB pins. For some of the connections, jumpers are soldered in place on the cape to provide a path to the appropriate Teensy and/or BBB pins. The tables list the jumper number for the pins.

Terminal J1 Connections to the Teensy:

J1 Terminal Position Connection Type Teensy Pin Teensy Pin Default Function Teensy Pin Serial Function
GND Direct GND GND –
0 Direct to Teensy and BBB 0 DIO 0 UART1 RX1
1 Direct to Teensy and BBB 1 DIO 1 UART1 TX1
2 R14 Jumper 2 DIO 2 –
3 R17 Jumper 3 DIO 3 –
4 R18 Jumper 4 DIO 4 –
5 R19 Jumper 5 DIO 5 –
6 R20 Jumper 6 DIO 6 –
7 R21 Jumper 7 DIO 7 UART RX3
8 R22 Jumper 8 DIO 8 UART TX3
9 R23 Jumper 9 DIO 9 UART RX2
10 R24 Jumper 10 DIO 10 UART TX2
11 R25 Jumper 11 DIO 11 –
12 R26 Jumper 12 DIO 12 –

 

Terminal J2 Connections to the Teensy:

J2 Terminal Position Connection Type Teensy Pin Teensy Pin Default Function
Vin Direct Vin Vin
AGN Direct AGN AGN
3.3V Direct 3.3V 3.3V
23 Direct via rectify circuit 23 Analog 9
22 Direct via rectify circuit 22 Analog 8
21 Direct via rectify circuit 21 Analog 7
20 R51 Jumper 20 Analog 6
19 R50 Jumper 19 Analog 5
18 R49 Jumper 18 Analog 4
17 R48 Jumper 17 Analog 3
16 R47 Jumper 16 Analog 2
15 R46 Jumper 15 Analog 1
14 R45 Jumper 14 Analog 0
13 None None None

 

Terminal J1 Connections to the BeagleBone Black:

J1 Terminal Position Connection Type BBB Pin BBB Pin Default Function BBB Pin Serial Function
GND Direct GND P8_1, P8_2, P9_1, P9_2, P9_43, P9_44, P9_45, P9_46 –
0 Direct to Teensy and BBB P9_24 GPIO_15 UART1 TX1
1 Direct to Teensy and BBB P9_26 GPIO_14 UART1 RX1
2 R37 Jumper P9_11 GPIO_30 UART4 RX4
3 R36 Jumper P9_12 GPIO_60 –
4 R35 Jumper P9_13 GPIO_31 UART4 TX4
5 R34 Jumper P9_14 GPIO_50 –
6 R33 Jumper P9_15 GPIO_48 –
7 R32 Jumper P9_16 GPIO_51 –
8 R31 Jumper P9_17 GPIO_5 –
9 R30 Jumper P9_18 GPIO_4 –
10 R29 Jumper P9_19 I2C2_SCL –
11 R28 Jumper P9_20 I2C2_SDA –
12 R27 Jumper P9_21 GPIO_3 –

 

Terminal J2 Connections to the BeagleBone Black:

J2 Terminal Position Connection Type BBB Pin BBB Pin Default Function
Vin Direct P9_5,P9_6 Vcc
AGN None None None
3.3V None None None
23 None None None
22 None None None
21 None None None
20 R44 Jumper P9_35 AIN6
19 R43 Jumper P9_36 AIN5
18 R42 Jumper P9_33 AIN4
17 R41 Jumper P9_38 AIN3
16 R40 Jumper P9_37 AIN2
15 R39 Jumper P9_40 AIN1
14 R38 Jumper P9_39 AIN0
13 None None None

Current Measurement Error

One period sampling window

The Teensy code should be written such that it samples the current for a time equal to the period of a single 60 hertz cycle (~0.016667 secs). This will guarantee that one (and only one) current peak will be measured since we don’t know the phase shift of the sampling window.
 

Max error occurs when sample straddles peak

The maximum measurement error occurs when the samples are taken 1/2 of the sampling interval from the peak of the current. Since the sampling window phase shift is not known, assuming the samples straddle the peak of the current provides the most conservative (worst case) current measurement error.
 

Error calculations

The maximum measurement error due to digitization can be calculated for a given sampling frequency as follows:
 

Example Error Values

Sampling Frequency (hertz) N Error %
300 5 19.10%
400 6.67 10.90%
1000 16.67 1.77%
3000 50 0.20%
6000 100 0.05%
10000 166.67 0.02%
12000 200 0.01%