About
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 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.
If you have one of the new Raspberry Pi Model B+ cards, we have a GVS card for the new Raspberry Pi Model B+ in Kickstarter now. If you have a Beaglebone Black we also have a GVS cape for the Beaglebone Black on Kickstarter now,
The RasPi-GVS card allows your Raspberry Pi to communicate with 5V devices by performing voltage translation from the 3.3V of the Raspberry Pi to 5V of GVS parts.
The RasPi-GVS card provides Ground, Voltage and Signal (GVS) connections to all of your 5V devices so you don't have to worry about power and ground routing from the Raspberry Pi 5V power signals.
This board 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.
The RasPi-GVS card can be used along with a breadboard for prototyping or in a deployed solution.
Features
- Daughtercard to the Raspberry Pi (you supply the Raspberry Pi)
- 3.3V to 5V bidirectional voltage translators on GPIO (General Purpose Input/Output) lines
- (7) 5V GPIO lines on GVS connectors
- (2) 5V SPI interfaces (can be used as 5 GPIO lines)
- (1) 5V UART (serial port) interface
- (1) 5V I2C interface (can be used as 2 GPIO lines)
- GPIO_4 enables/disables the voltage translators
-
Resettable Fuse protection on the 5V power lines
- 5V Power Supply which can power the GVS connectors (within limits)
- Jumper to select power for GVS (allows the GVS connectors to be powered from either the on-board regulator or powered from the Raspberry Pi)
- 49x49mm card form factor
Voltage Translators
The Raspi-GVS board uses Texas Instrument TXS0108 voltage translators.
Voltage Translators Feature
- 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
What is GVS?
GVS is great for prototyping or deploy-able products. The beauty of the GVS connection is that power and ground are provided with each I/O signal. That provides the power needed to power external sensors and output devices. Otherwise splitting the one or two power pins into separate cables ends up being a real mess.
GVS stands for Ground, Voltage and Signal. It's a 3-pin unofficial standard. It uses 0.1" pitch pins. There are a large number of GVS sensors (inputs) and devices (output) parts on ebay although they are not called GVS sensors typically. They are identifiable by the three pins and the silkscreen near the pins as GVS sensors. Even sensors which don't have the GVS pin ordering can still be used they just require a cable with wiring other than 1:1.
Testing
Our video (top) shows that we were able to set all 14 GPIO channels to outputs and write one of the channels at a time. Our test code is here.
The only thing remaining was testing the UART lines. We found this page and when we tried it the UART worked as well.
All in all, we are confident that this is a fine card.
Risks and challenges
We built a prototype card and it works great. We have local talented assemblers and feel comfortable that we can scale production if this project is funded.
The card has some mechanical challenges since there are no mounting holes. We put some double stick tape on the back of the board to keep it from shorting to the capacitor and HDMI connector below the card.
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Funding period
- (32 days)