- 1 Board Design
- 2 Connectors
- 2.1 P1 - Raspberry Pi GPIO Connector
- 2.2 J1 - I2C bus
- 2.3 J2 - UART I/F
- 2.4 J3 - IO_18 GVS
- 2.5 J4 - IO_17 GVS
- 2.6 J5 - IO_27 GVS
- 2.7 J6 - IO_23 GVS
- 2.8 J7 - IO_22 GVS
- 2.9 J8 - IO_24 GVS
- 2.10 J9 - IO_25 GVS
- 2.11 J10 - SPI0 (Serial Peripheral Interface)
- 2.12 J11 - SPI1 (Serial Peripheral Interface)
- 2.13 DC Power 7-9 VDC
- 2.14 J13 - Power Select
- 3 Parts List / Assembly Sheet
- 4 Factory Tests
- 5 Rev X3 Board
- 6 Rev X2 Board
- 7 Rev X1 Board
Like a lot of folks we got excited when the Raspberry Pi was first announced. We couldn't wait to get our hands on our first board. When our chance came to get a Pi we also bought a prototyping board so we could connect up our own devices to the Pi. We anxiously awaited the arrival of our card. It felt like our card would never arrive.
While we were waiting, we dug deeper and found out that Raspberry is limited to 3.3V I/O and we realized that the GVS devices we already have for our Arduinos are 5V parts that would not work with our Raspberry Pi. Sure we could adapt one of the 3.3V to 5V converters out there but that sounded like a lot of work. What we really wanted was a way to allow our 5V GVS parts to connect to the Raspberry Pi without a lot of hand wiring but we couldn't find a card out there that does the 3.3V to 5V voltage conversion that our 5V parts need.
So we designed a card to meet our needs, the Raspberry Pi-GVS Card.
The RasPi-GVS card is modeled on the Arduino Sensor Shields, also known as GVS shields. Arduino Sensor Shields bring out the pins of the Arduino to GVS (set of Ground, Voltage and Signal) pins. Unfortunately, the Raspberry Pi can't work with the same 5V GVS devices as the Arduino since the Raspberry Pi has 3.3V I/O.
The RasPi-GVS card allows the Raspberry Pi to communicate with the same 5V sensors by performing voltage translation from the 3.3V of the Raspberry Pi to 5V.
- 3.3V to 5V bidirectional voltage translators on Raspberry Pi GPIO lines
- (7) 5V GPIO lines on GVS connectors
- (2) 5V SPI interfaces (can be used as 5 GPIO lines)
- (1) 5V UART interface
- (1) 5V I2C interface (can be used as 2 GPIO lines)
- GPIO_4 enables/disables the voltage translators (active high)
- Power Supply which can optionally power the GVS connectors
- 49x49mm card form factor
The Raspi-GVS board uses Texas Instrument TXS0108 voltage translators.
Voltage Translators Features
- No Direction-Control Signal Needed
- Max Data Rates
- 60 Mbps (Push Pull)
- 2 Mbps (Open Drain)
- 1.2 V to 3.6 V on A Port and 1.65 V to 5.5 V on
- B Port (VCCA ≤ VCCB)
- No Power-Supply Sequencing Required –
- Either VCCA or VCCB Can Be Ramped First
- Latch-Up Performance Exceeds 100 mA Per JESD 78, Class II
- ESD Protection Exceeds JESD 22 (A Port)
- 2000-V Human-Body Model (A114-B)
- 150-V Machine Model (A115-A)
- 1000-V Charged-Device Model (C101)
- IEC 61000-4-2 ESD (B Port)
- ±6-kV Air-Gap Discharge
- ±8-kV Contact Discharge
Voltage Translators Architecture
The TXS0108E can be used in level-translation applications for interfacing devices or systems operating at different interface voltages with one another. The TXS0108E is ideal for use in applications where an open-drain driver is connected to the data I/Os. The TXS0108E can also be used in applications where a push-pull driver is connected to the data I/Os, but the TXB0104 might be a better option for such push-pull applications. The TXS0108E device is a semi-buffered auto-direction-sensing voltage translator design is optimized for translation applications (e.g. MMC Card Interfaces) that require the system to start out in a low-speed open-drain mode and then switch to a higher speed push-pull mode.
To address these application requirements, a semi-buffered architecture design is used and is illustrated above (see Figure 1). Edge-rate accelerator circuitry (for both the high-to-low and low-to-high edges), a High-Ron n-channel pass-gate transistor (on the order of 300 Ω to 500 Ω) and pull-up resistors (to provide DC-bias and drive capabilities) are included to realize this solution. A direction-control signal (to control the direction of data flow from A to B or from B to A) is not needed. The resulting implementation supports both low-speed open-drain operation as well as high-speed push-pull operation.
When transmitting data from A to B ports, during a rising edge the One-Shot (OS3) turns on the PMOS transistor (P2) for a short-duration and this speeds up the low-to-high transition. Similarly, during a falling edge, when transmitting data from A to B, the One-Shot (OS4) turns on NMOS transistor (N2) for a short-duration and this speeds up the high-to-low transition. The B-port edge-rate accelerator consists of one-shots OS3 and OS4, Transistors P2 and N2 and serves to rapidly force the B port high or low when a corresponding transition is detected on the A port.
When transmitting data from B to A ports, during a rising edge the One-Shot (OS1) turns on the PMOS transistor (P1) for a short-duration and this speeds up the low-to-high transition. Similarly, during a falling edge, when transmitting data from B to A, the One-Shot (OS2) turns on NMOS transistor (N1) for a short-duration and this speeds up the high-to-low transition. The A-port edge-rate accelerator consists of one-shots OS1 and OS2, Transistors P1 and N1 components and form the edge-rate accelerator and serves to rapidly force the A port high or low when a corresponding transition is detected on the B port.
The RaspPi-GVS offers flexible power supply options. The 5V for the GVS Connnectors and translators can come either from the Raspberry Pi or from the 5V power supply on the RaspPi-GVS.
A three pin header and jumpers are used to select the voltage source(s). Installing a single jumper from pins 2 to 3 allow the Raspberry Pi to power the GVC connectors and voltage translators. Installing a jumper from 1 to 2 powers the GVS connections and voltage translators from the 5V power supply.
P1 - Raspberry Pi GPIO Connector
J1 - I2C bus
J2 - UART I/F
J3 - IO_18 GVS
J4 - IO_17 GVS
J5 - IO_27 GVS
J6 - IO_23 GVS
J7 - IO_22 GVS
J8 - IO_24 GVS
J9 - IO_25 GVS
J10 - SPI0 (Serial Peripheral Interface)
- MOSI (GPIO_10)
- MISO (GPIO_9)
- SCK (GPIO_11)
- CE0 (GPIO_8)
J11 - SPI1 (Serial Peripheral Interface)
- MOSI (GPIO_10)
- MISO (GPIO_9)
- SCK (GPIO_11)
- CE1 (GPIO_7)
DC Power 7-9 VDC
- Shell - Ground
- Center - Power (7-9 VDC)
J13 - Power Select
- 1-2 = Power GVS and voltage translators from the voltage regulator on the RasPi-GVS
- 2-3 = Power GVS and voltage translators from the Raspberry Pi
Parts List / Assembly Sheet
If No DC Power
|1||CONN_3||Jumper J13 from 2-3|
If DC Power
- Unit Under Test (UUT)
- Cable set
- Cable up card
- Mount on RPI_PSOC5
- Connect RPI_PSOC5 to PC
- LED should be blinking on RPI_PSOC5 card
- Find USB Serial Port
- Type ? for menu
- Select card from menu
- W - to write EEPROM
- R - to read EEPROM
- B - to bounce a light across the LED card(s)
- Turn off card
Rev X3 Board
Rev X2 Board
- Ordered from OshPark
Rev X1 Board
- Rev X1 board works.