I welcome you to this part of my RoadTest review about Bridgetek BT817 evaluation board. In this chapter I will describe board itself. I will not describe BT817 chip and its features here because chip is described in dedicated chapter Review of Bridgetek BT817 Embedded Video Engine. Except these two chapters there are main page (marked with yellow star in following table of contents) with final summary and score, two project description and one tutorial. All parts of my review are linked in following table of contents:
- Introduction, contents, summary, and score
- Review of Bridgetek BT817 Embedded Video Engine
- Review of Bridgetek ME817EV Evaluation Board (this page)
- Pacman using Bridgetek BT817
- How does the BT817 coprocessor work?
- ZUSI 3 display (become available in the future)
BT817 Evaluation Board also referred as ME817EV is board evaluating BT817 Graphics Engine designed to be used within devices requiring display input/output. At beginning I likely to describe what interesting parts we can find on reviewed board.
The main chip is not the largest one on this board. BT817 chip is highlighted on following image:
The largest chip is FIN3385 originally from Farchild Semiconductor, but Farchild Semiconductor was acquired by ON Semiconductor, so now you can find official datasheet at their website. This chip is used to convert RGB parallel data signals to LVDS interface. BT817 does not support LVDS but this chip makes LVDS interface on this board available. Chip is highlighted on following image:
Next chip near to main BT817 chip is external flash memory. It is 16MiB (128 Mib) serial flash memory from Winbond. This flash memory can be used for storing some large assets like fonts and bitmaps without need them stored in program memory of your microcontroller. Memory is connected directly to BT817 and can directly access stored assets stored in this memory. Flash memory is highlighted on following image:
The chip which is located in the bottom right corner near right USB Type-C port is FTDI FT4222HQ. This chip is connected to the control QSPI bus of BT817 and allows you to command BT817 from the computer over USB without need to programming any external microcontroller. FT4222 is highlighted on following image:
The chip in top left corner is TPA6205A1 audio amplifier from Texas Instruments. Note that board have no speaker, but you can connect your own external one using connector which is near to this chip. Amplifier is highlighted on following image:
All other chips are used for powering board and display. TFT LCD displays requires multiple voltage usually referred as VGH and VHG, VCOM and also independent voltage for powering analog parts of display. Some of these voltages are pretty high (about 15V) and some of them are also negative (about -6V). Board must also power backlight LEDs and finally, it must generate voltage for powering all digital parts including main BT817 chip. Evaluation board can generate all these voltages. The most advanced powering chip is TPS65145 which is responsible for most advanced voltages like mentioned high voltage and negative voltage. It is highlighted on following image:
Powering backlight LED is managed by IS31BL3506A from Lumissil. It is boost converter connected in a way that regulates voltage to drive LEDs with constant current. Current flowing by LEDs is adjustable using switches. Regulator and switches are highlighted on following image:
The main supply for digital circuits is generated by AOZ1282CI regulator. This regulator generates 3.3V. You can also choose 2.5V using jumper for powering digital parts of display. In this case 2.5V is generated by MIC5504 LDO. Both regulators are highlighted on following image:
Except chips there are lot of connectors. They are used for connecting different types of display, touch controllers of displays and audio speaker. Except connectors related to attached display there are two USB Type-C ports. Both can be used for powering board and right port is also connected to FT4222.
Third powering option is using is using 5V input at host control connector which you can use for connecting your own external microcontroller. This connector is very important to all developers and it highlighted on following image:
Modes of operations
Board allows two methods of interacting with BT817 allowing use it by two different approaches. The first approach is that you connect your own Microcontroller (STM32, Cypress PSoC, Atmel/microchip AVR, PIC16, …) to the connector highlighted on previous image and then you issue commands by your microcontroller. This is most desired way of how BT817 chip can be utilized in real world, but this development board allows one more very interesting approach. All signals which are usually connected to your MCU are also connected to the FTDI FT4222HQ chip. You can disconnect them using switches and you should do that when using board in conventical way with your own MCU. But if you connect them, you can access BT817 signals from your computer over USB without need of any external Microcontroller. FT4222 is usually USB-to-UART converter but FT4222 is advanced model in FT family which have special processor that can be used as a USB-to-GPIO, USB-to-I2C, USB-to-JTAG, and of course USB-to-QSPI which is utilized on this board. So, you can issue drawing commands to the BT817 chip from your PC without need of any external microcontroller and this is nice.
As I have mentioned in the previous section, powering cascade is very complex. Board generates lot of voltages and most of them are configurable using trimmers. This allows you to use board with almost any display (with compatible RGB or LVDS interface). I have seen some boards with RGB interface with fixed voltages and some unconnected powering pins, but this is not a case of this board. Boards with some fixed or unconnected voltages are usually restricted to some specific display but as I stated this is not case of RoadTested board which is very flexible. Voltages referred as VGH, VGL, VCOM and AVDD are configurable within boundaries used by most display. Voltages are configurable using small SMD trimmers. Trimmers are available near to related power regulators. It is hard to find them when you are looking to the board first time. There are also no notices that you should check its configuration before powering board with display connected. In my case they come preconfigured from the factory to voltages very near voltages which I needed for my display. You need screwdriver to configure them. It is mostly impossible to configure them by hand without screwdriver. They are small and do not occupy lot of space vertically. Because board was designed also for embedding inside device and not just an evaluation board, I accept less user-friendly trimmers. Near every configuration trimmer there are test points which can be used for checking configured voltage. Trimmers for configuring voltages are highlighted on following image.
Mostly I am satisfied with very flexible powering options on this board, but I think Bridgetek should spend more effort with documenting it.
There are multiple connectors which I assign to five categories and some of them I have already described in previous sections. Categories are:
- USB Type-C connectors
- Host (external MCU) connectors
- Display connectors
- Touch controller connectors
- Speaker connector
Display and touch controller connectors are designed and located for use with some common specific display. For example, position of RGB interface connector and touch controller connector exactly matches lengths and locations of flex cables used on Riverdi TFT displays. No flex cable is bend and no reduction or similar “hack” is needed. Board is very user friendly when used with some of these common displays.
There are two connectors for connecting external microcontroller to this board. The first one is standard 2.54mm pinhead in the center of board. Second connector with same signals is at the right side of board and you can interconnect your board with this board using flexible cable. You can choose if you want to use pinhead or flexible cable. Connectors are equivalent. You can for example use pinhead at development time and flex cable at production time.
There are 6 connectors used for connecting touch controllers. Two of them are used for testing purposes and are not soldered. Remaining four are connected to the same signals but they are different type, and they are in different locations so you can choose whatever you want. Usually, you select the one which fits with your display.
Lastly there are audio connector which is connected to the audio amplifier and you can use it for connecting to the speaker. There are only one audio connector and no alternatives like we have seen in previous paragraph about touch controller connectors which are present in multiple variants. Connector is normalized 1.5 mm pitch. This is fine if you own some compatible cable, but I had to bought one. Because it does not still arrive yet (I bought it on Aliexpress…) so I did not try this feature at RoadTest time, and I will try it in the future. It would be nice to have accessible audio output on some more common connector like 2.54mm pinhead. The reason for omitting other audio connector most probably was need for noise reduction on analog audio lines, so I accept this and do not consider this as a disadvantage.
There are two jumpers. Both are related to powering. First is used to select main power supply source for generation of other voltages using regulators. Second jumper is used 2.5V or 3.3V for powering digital parts of display.
Board is properly labelled. Silkscreen quality is not the best one, but labels are readable. Letters are not placed over vias. I did not find any deformed letter. Connectors are described with user friendly labels. Jumpers also are. The only thing which should be described better are trimmers and test points. There are reference designators but meaning of trimmer and test point you must search in documentation manually. It would be nice to have some silkscreen labels that describe its purpose here.
There are two holes for routing flex cables from back side to front side. You can use them with Riverdi TFT displays. Except holes there are multiple types of mounting points. Documentation has mechanical drawing with exactly specified dimensions.
There are onboard amplifier and connector for connecting external speaker. As I have mentioned above, I did not received bought cable with compatible connector yet, so I did not try this feature yet, but I expect that everything will be fine for embedded usage. Of course, if you require ultra-high audio quality, then you most probably won’t be satisfied with 8-bit output from BT817. I will try this feature later. If I found some issue later when I will try this feature, I will update this section later, but for now, I do not expect any issues.
I will describe software more in chapter Review of BT817 Graphics Accelerator and I will briefly describe only software related to board here.
There are available great SDK with comprehensive set of examples. SDK and demonstration projects support executing commands using onboard FT4222 USB-to-QSPI, so you can see supported features just by connecting to computer over USB. Board is natively supported by SDK. Only change what you need to do is specifying display resolution because this board is not a fixed to some display and you can use it with display which fits your own requirements.
Documentation is not very complex but is very user friendly and readable. In this chapter I will only documentation related to board. Documentation related to BT817 chip I will describe in chapter Review of BT817 Embedded Video Engine. This practically mean that only document which I will describe here is board datasheet which can be partially considered as a user manual.
Board datasheet contains all information which I required when working with board. It is very user friendly and describes all important thing clearly in a short manner. Document contains description of board, description of onboard components, contains drawing of both bottom and top PCB layer, description of all jumpers and connectors, has schematic and contains tutorial describing how to configure and use board in multiple manners. Finally, there are basic electrical specifications. Most content is very high quality, correct and I like it. I have only one note there. Schematic is pasted to this document as very low-quality screenshot. Search feature of PDF viewer does not work here because it is screenshot. I recommend exporting schematic as separate PDF document like some other vendors do that. Except technical issues with schematic, it is well drawn, and it is easy to understand schematic.
Board came properly packaged in antistatic bag and compact paper box. Board was properly secured. Packaging do not contain any other things. As part of RoadTest We have received display, but normally this evaluation board is not bundled with any display and you must buy display on your own expense. This can be also classified as benefit because you can use whatever display you want including display with non-standard resolutions which may be very interesting in many embedded applications. Packaging also do not contain USB cable, which is usually bundled with evaluation boards. But because board is also designed for production use inside embedded device, I consider lack of USB Type-C cable acceptable.
Cost and Availability
Board is available for 116 USD at official site and about 120 USD at Newark and about 100 USD at other distributors. Prices are valid at the time of writing this review. Very interesting to me is that Bridgetek products are available at many small local European distributors. Usually only big vendors like Farnell brings us this kind of hardware, but Bridgetek products (both ME817EV evaluation board and BT817 chip) are available at smaller local distributors also. Second good thing is that even at the time of component supply shortage crisis both evaluation board and BT817 graphics engine are in stock at almost all distributors.
I liked this board very much. I did not find any significant issue. The most significant issue that annoyed me was emplaced schematic inside manual without possibility to search for occurrences inside it. Technically board is good. There are very interesting onboard components. Board support broad range of displays and integrates USB-to-QSPI bridge allowing very interesting and unique use cases. It is good evaluation board and I like it.