Archive for the ‘Periphery’ Category.

Adding RS485 to FRDM-K64F

FRDM-K64F is nice piece of development board. Unfortunately, it is “bonded” to MBED development platform, which is a nightmare! Adding RS485 “out of the box” to the FRDM-K64F in MBED is NoGo. But it is very easy.

Here is image from my scope sending single char via UART4 with enabled RTS as DE for RS485 in Half Duplex mode:

scope_0

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SiLabs Si7013 humidity and temperature sensor

I got samples of Si7013.

The Si7013 I2C Humidity and 2-Zone Temperature Sensor is a monolithic CMOS IC integrating humidity and temperature sensor elements, an analog-to-digital
converter, signal processing, calibration data, and an I2C Interface. The patented use of industry-standard, low-K polymeric dielectrics for sensing humidity enables the construction of low-power, monolithic CMOS Sensor ICs with low drift and hysteresis, and excellent long term stability. The humidity and temperature sensors are factory-calibrated and the calibration data is stored in the on-chip non-volatile memory. This ensures that the sensors are fully interchangeable, with no recalibration or software changes required. An auxiliary sensor input with power management can be tied directly to an external thermistor network or other voltage-output sensor. On-board logic performs calibration/linearization of the external input using user-programmable coefficients. The least-significant bit of the Si7013’s I2C address is programmable, allowing two devices to share the same bus. The Si7013 is available in a 3×3 mm DFN package and is reflow solderable. The
optional factory-installed cover offers a low profile, convenient means of protecting the sensor during assembly (e.g., reflow soldering) and throughout the life of the product, excluding liquids (hydrophobic/oleophobic) and particulates. The Si7013 offers an accurate, low-power, factory-calibrated digital solution ideal for measuring humidity, dew-point, and temperature, in applications ranging from HVAC/R and asset tracking to industrial and consumer platforms.

I prepared prototyping board with STM32F0 and line RS485 driver:

rht  pcbrht0

 

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Simple WEB server hosted on NXP/Freescale FRDM K64F demo board

Kinetis K64F demo board is excellent little board for experimenting with ethernet. There is no quick step-by-step tutorial for building simple web server on this board. The following instructions help bringing working HTTP server on FRDM K64F with one index page and second page with simple CGI script to print out some random numbers. This is absolute minimum for developing any web based gadget with this board.

frdm-k64f120m-board-with-bluetooth-and-nrf24l01

(image source: https://mcuoneclipse.com/2014/04/09/ftf-frdm-k64f-kinetis-design-studio-and-kinetis-sdk/ )

What you will need:

  • Compiling tool: Keil development tools
  • Hardware:
  • Good to read: HTTP server demo application
  • LAN cable and spare port on your switch or router

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RGB LED Badge

This is heart shaped four RGB led badge:

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USB to Alphanumeric LCD interface

This is simple, small interface between USB and alphanumeric LCD with 16×2 characters. It is using CDC class – Virtual COM port.

Microcontroller is from STM32 cortex M0 value line family: STM32F070F6. This small “gizmo” has very attractive price and good choice of peripheral devices, like ADC, USB, plenty of timers, etc… Really nice device in “DIY-friendly” package – TSSOP20.

f0 pcb-asm test

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Ultra low cost I2C level shifter

I have some I2C sensors which are capable of running from low supply voltages. Host microcontroller has 3,3 or 5V supply, which is usually out of absolute maximum range, when I2C device is supplied with e.g. 1,8V. The sensor is usually very low power, which means simple emitter follower could do the low voltage supply.

The circuit schematic is shown in following drawing (click to enlarge):

sch

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MODEM, parrot, CAT, …

Full bunch of wires is hanging from each HAM station and PC connected to the station: CAT, audio, each via dedicated interface for isolation or level shifting. Additional mess is with parrots or digital interfaces for digital mode. I wanted simple solution, which can be conected to PC via single USB cable.

I was looking for simple audio CODEC and found WM8731. To have enough processing power for some simple DSP audio I chose cortex M4F microcontroller. There is also micro-SD on the board for audio recording and playback, two mini-DIN connectors with YAESU pinout and galvanic isolation for USB. I stareted this project few months ago. I will add posts when I will make progress with module programming.

modem

The PCB is 80x45mm.

Here is schematic: modem

And PCB layout: lingva

 

Stay tuned for further progress reports.

 

The software will be published on git.

16 bit ADC (AD7715) prototyping board

AD7715AD7715:

The AD7715 is a complete analog front end for low frequency measurement applications. The part can accept low level input signals directly from a transducer and outputs a serial digital word. It employs a Σ-Δ conversion technique to realize up to 16 bits of no missing codes performance. The input signal is applied to a proprietary programmable gain front end based around an analog modulator. The modulator output is processed by an on-chip digital filter. The first notch of this digital filter can be programmed via the on-chip control register allowing adjustment of the filter cutoff and output update rate. The AD7715 features a differential analog input as well as a differential reference input. It operates from a single supply (3 V  or 5 V). It can handle unipolar input signal ranges of 0 mV to 20 mV, 0 mV to 80 mV, 0 V to 1.25 V and 0 V to 2.5 V. It can also handle bipolar input signal ranges of ±20 mV, ±80 mV, ±1.25 V and ±2.5 V. These bipolar ranges are referenced to the negative input of the differential analog input. The AD7715 thus performs all signal conditioning and conversion for a single channel system. The AD7715 is ideal for use in smart, microcontroller, or DSP-based systems. It features a serial interface that can be configured for three-wire operation. Gain settings, signal polarity, and update rate selection can be configured in software using the input serial port. The part contains self-calibration and system calibration options to eliminate gain and offset errors on the part itself or in the system.

Protoboard is assembled with AD7715 and precision voltage reference REF5025. The AD7715 is ideal for bridge applications (like weigh scales, pressure transducers, thermometers, etc…) with ratiometric differential input and integrated PGA. PCB is single-sided.

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Universal ethernet PHY

Ethernet PHY is required in every microcontroller application which uses ethernet interface. It consists of RJ45 connector, transformers and PHY controller, which is analog circuit – interface between transformers and ethernet controller in microcontroller.

Circuit is divided in two PCB to keep it simple and single-sided. It connects via 20 pads (2,54mm raster) in dual row. Ethernet cables are usually stiff.  Dual-in-line style of this module provides better mechanical rigidity.

Ethernet PHY module

Universal ethernet PHY module

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Micro SD breakout board

This micro SD brekout board is usefull to connect micro-SD card to 2,54 mm header. Schematic is extremely simple:

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