9 Nov 2021

LDs Should Be Powered By Constant Current Sources

by admin | posted in: Technology | 0

Semiconductor laser diodes are very fragile and can be damaged by improper use. Overheating and overcurrent can cause the laser diode to experience rapid light decay or be damaged on the spot in a short period of time.

Laser diodes respond very quickly to overvoltage/overcurrent, and short-term (ns-level) overloads can also cause damage, which is especially noteworthy.

Like normal diodes, laser diodes also have a fairly steep I-V curve, which means that when the supply voltage deviates slightly from the rated voltage, the current will change drastically, even causing it to burn out. More seriously, as the temperature changes, the rated operating voltage and rated power of the laser diode also change. Therefore, the constant voltage source is unreliable, and the constant current source is the best choice.

Laser diodes are sensitive to dust, so make sure you assemble the mirror set in a super clean room.

Laser diodes are also sensitive to the returning power, so make sure that your fiber optic connectors or lens have a low enough reflection coefficient, which can often be achieved by coating.

9 Nov 2021

Advanced Versatile Handheld Oscilloscope

by admin | posted in: Photos | 0

We have been working on designing small and compact handheld multifunction oscilloscopes based on the following points:

1. The large volume of the instrument occupies too much space, which is not conducive to the performing of the experiment.

2. Many applications, such as equipment debugging, automobile maintenance, outdoor operation, testing wireless modules in open areas, etc., require portable instruments.

3. Students need a low-cost, compact oscilloscope that is easy to bring to home and school.

We have designed several multifunctional handheld instruments, usually including at least three parts: the wave oscilloscope, the signal generator and the programmable power supply.

Earlier, we did some prototypes of the low-cost oscilloscopes.

We also planned to make a large benchtop oscilloscope with a lot of input and output channels for in-line measurements on the production line.

11 Oct 2021

Made an RFID Tester – for HF&UHF Tags

by admin | posted in: Sharing, Technology | 0

The high-frequency/radio-frequency cards (tags) are widely used, such as financial payment, access management, product traceability, workshop positioning, inspection records, etc.

These HF type cards mainly work in the 13.56MHz frequency band and include multiple protocols, such as 15693, 14443A\B, etc.

The RF performance and protocol conformance testing are quite important parts in the design and production process of HF/UHF cards and readers.

We used Xilinx’s FPGA to implement a low-cost RFID characteristic tester, and completed the corresponding C# host computer software.

The parameters are as follows:

① Spartan 3E-1200K main controller, onboard RAM and ROM.

② The highest rate of the UART interface is up to 1.5Mbps, which is used for PC communication.

③ 0-30MHz arbitrary waveform generator, built-in 165Msps 12bit DA converter, which can provide the voltage range of 50mVp-p to 10Vp-p between the frequency of 0-15MHz.

④ The 100MH bandwidth 12bit AD converter can perform low-pass and band-pass sampling.

⑤ Used for 13.56MHz ISO15693, ISO14443 and other high-frequency RFID transceiver test, signal modulation and demodulation analysis, and carrier generation.

⑥ It can be used for the processing and analysis of 915MHz baseband signals or down-conversion signals.

The design of the tester is very complex, and even includes frequency analysis, modulation analysis, protocol analysis, etc. at higher frequencies.

Based on this equipment, we have developed another very high-end RFID test board, using the 14-layer microwave Rogers PCB and Xilinx SOC chip ZYNQ, which contains ARM A9 processors and a powerful FPGA. It supports the QAM modulation and demodulation with frequencies up to 2.4GHz carrier. Besides, we also designed a circular polarization cut-angle microstrip antenna for 915MHz.

FPGA module framework for VHDL design.

9 Oct 2021

Local Multipoint Transport Protocol（LMTP）

by admin | posted in: Technology | 0

LMTP is a communication protocol designed by us and is used for the pluggable bus structure inside the instrument. This protocol is suitable for the local multi-point high-speed communication occasions such as industrial control facilities and the interior of instruments.

Features:
※ 400MB/S peak transfer rate
※ Up to 32 devices can be connected (when W=32)
※ Bus sharing, time division multiplexing
※ Applicable to “one master, multiple slaves” or “peer-to-peer” structure
※ Asynchronous request, synchronous transmission
※ Single/Burst Mode/DMA Transfer
※ Low power consumption, the clock is only valid during transmission
※ The bus address/token can be configured externally
※ Optional serial configuration bus, hot-plug support

LMTP v2 does not specify the bus width and the number of base address bits, that is, it applies to the case of [8/16/32] bits, but each device in the same transmission system must be consistent. By default, this protocol uses a 32-bit bus width and a 3-bit base address system as an example; LMTP v2 does not specify the transmission voltage level, but each device in the same transmission system must also be consistent.

LMTP v2 includes two parts: high-speed parallel line and serial configuration line. The serial configuration line is equivalent to the universal asynchronous transceiver UART, so this document mainly introduces the high-speed parallel line.

The high-speed devices with fixed configurations can use the high-speed parallel line alone, while the low-speed devices that do not require high-speed transmission can use the serial configuration line alone. LMTP v2 is especially suitable for the devices with multiple [MCU/APU+FPGA] architectures.

Bus symbols	Definition	Default level	Active level
RAD	请求/地址/数据公共总线	非驱动弱上拉	请求期间低电平发起传输请求；传输期间推挽有效
OCPY	总线占用标志	非驱动弱上拉	低电平标志总线被发起设备占用；【OCPY逻辑与RVD】有效表示总线被占用
CMD	总线命令	非驱动弱上拉	传输期间推挽有效
CLK	总线时钟	非驱动弱上拉	总是由发起设备驱动，第一个下降沿确保地址建立；传输完成后产生一个额外周期后恢复高电平
RVD	远端设备回应数据有效，即”读”有效	非驱动弱上拉	低电平表示远端设备正驱动总线
WVD	发起设备驱动总线有效，即”写”有效	非驱动弱上拉	低电平表示发起设备正在驱动总线
INT	中断请求	非驱动弱上拉	低电平表示有设备发起中断请求，该线路采用OC形式，只可驱动为低
RST	总线设备复位	非驱动弱上拉	低电平器件所有设备复位
TX	可选串行配置发送	驱动为高	低电平起始位有效
RX	可选串行配置接收	非驱动弱上拉	低电平起始位有效

Example board design based on LMTP:

Articles Full

Semiconductor laser diodes are very fragile and can be damaged by improper use. Overheating and overcurrent can cause the laser diode to experience rapid light decay or be damaged on the spot in a short period of time.

Laser diodes respond very quickly to overvoltage/overcurrent, and short-term (ns-level) overloads can also cause damage, which is especially noteworthy.

Laser diodes are sensitive to dust, so make sure you assemble the mirror set in a super clean room.

Laser diodes are also sensitive to the returning power, so make sure that your fiber optic connectors or lens have a low enough reflection coefficient, which can often be achieved by coating.

We have been working on designing small and compact handheld multifunction oscilloscopes based on the following points:

1. The large volume of the instrument occupies too much space, which is not conducive to the performing of the experiment.

2. Many applications, such as equipment debugging, automobile maintenance, outdoor operation, testing wireless modules in open areas, etc., require portable instruments.

3. Students need a low-cost, compact oscilloscope that is easy to bring to home and school.

We have designed several multifunctional handheld instruments, usually including at least three parts: the wave oscilloscope, the signal generator and the programmable power supply.

Earlier, we did some prototypes of the low-cost oscilloscopes.

We also planned to make a large benchtop oscilloscope with a lot of input and output channels for in-line measurements on the production line.

The high-frequency/radio-frequency cards (tags) are widely used, such as financial payment, access management, product traceability, workshop positioning, inspection records, etc.

These HF type cards mainly work in the 13.56MHz frequency band and include multiple protocols, such as 15693, 14443A\B, etc.

The RF performance and protocol conformance testing are quite important parts in the design and production process of HF/UHF cards and readers.

We used Xilinx’s FPGA to implement a low-cost RFID characteristic tester, and completed the corresponding C# host computer software.

The parameters are as follows:

① Spartan 3E-1200K main controller, onboard RAM and ROM.

② The highest rate of the UART interface is up to 1.5Mbps, which is used for PC communication.

③ 0-30MHz arbitrary waveform generator, built-in 165Msps 12bit DA converter, which can provide the voltage range of 50mVp-p to 10Vp-p between the frequency of 0-15MHz.

④ The 100MH bandwidth 12bit AD converter can perform low-pass and band-pass sampling.

⑤ Used for 13.56MHz ISO15693, ISO14443 and other high-frequency RFID transceiver test, signal modulation and demodulation analysis, and carrier generation.

⑥ It can be used for the processing and analysis of 915MHz baseband signals or down-conversion signals.

The design of the tester is very complex, and even includes frequency analysis, modulation analysis, protocol analysis, etc. at higher frequencies.

FPGA module framework for VHDL design.

LMTP is a communication protocol designed by us and is used for the pluggable bus structure inside the instrument. This protocol is suitable for the local multi-point high-speed communication occasions such as industrial control facilities and the interior of instruments.

LMTP v2 includes two parts: high-speed parallel line and serial configuration line. The serial configuration line is equivalent to the universal asynchronous transceiver UART, so this document mainly introduces the high-speed parallel line.

Example board design based on LMTP: