Monthly Archives: March 2015

Processor Option 3

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The MSP432P401RIRGC is an ARM Cortex M4F processor.  It has a web based IDE (integrated development environment). It has six serial communication modules and runs up to 48 MHz. This chip started out looking good, however it doesn’t look very good after a little bit of research.  A quick look back at the Microchip processor (Processor Option 2) showed me that this processor is probably not a good fit for this design.  Unless I eliminate the other processor options, I will not use this chip.  The chip not being available yet plays a large part of this decision. If it becomes available before I start prototyping, I may change my mind.

Side Note:

For my abbreviations I will always use an upper case B to represent bytes and a lower case b to represent bits.  For instance 1,000 bytes will be represented as 1 KB and 1,000,000 bits will be represented at 1 Mb.

 

MSP432P401RIRGC

Device Advantages

  • SPI up to 16Mbps with DMA
  • 256 KB Flash code space
  • 64 KB RAM space (16 bit address pointers are very easy to work with in C)

Device Disadvantages

  • Not available yet
  • Large pin count (64 pin for smallest variant)
  • No DIP part for prototyping
  • US $5.59 in quantities of 1K (Kind of high) may come down when released.

 

Experience and Heuristic method

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Experience gives us a better chance at guessing solutions to a problem.

For instance a 220 Ohm resistor is a good rule of thumb for an LED current Limiting resistor in a 5 volt circuit.  A simple guess for a 10 volt circuit would be to just double the resistance to around 440 ohms.  Unfortunately this will probably burn out the LED.  From experience of doing the calculations, you would recognize that a 1000 ohm resistor usually works well in a 10 volt circuit.

Heuristic method comes in to play when you are working in an area that you are less experienced in.  You look at how similar operating circuits have worked in the past and make an educated guess to design the new circuit. Sometimes you just make a guess and then test, even with no reasoning as why that guess would work.

So if you are a tinkerer or an engineering student, go get some experience. Go build some circuits, make some changes, break something, then try to fix it or maybe improve it.

Happy π Day

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Today, Saturday March 14th 2015 is Pi day.  The first 5 digits of Pi(3.1415) can be used to represent today’s date. Pi is the ratio of the circumference of a circle to it’s diameter.  Although Pi is defined in reference to a circle, Its value is used in many branches of mathematics.

As an engineer or tinkerer, mathematics is important. Don’t let that scare you if you aren’t good at math.  We are in a unique position in history. The internet has made lots of information available at your fingertips.  This means that as long as your not on the cutting edge of design, you can usually find the information you need without having to do the calculations yourself.

As a professional engineer, you are more valuable to your employer(even if you are self employed) if you understand the key math to your project.  If you don’t know some of the principle math for a project, you can use reference designs for the section you don’t understand. You can use modelling software to modify your design before prototyping. You can go to online courses like Khan Academy that will help you understand the concepts. If you are a tinkerer or an engineer, I highly recommend you practice using your preferred search engine – Keep refining your search when you don’t find what you are looking for.

The universal programmer design that needs basic understanding of the math necessary to work out Ohms Law and simple logic. The complex math necessary for understanding the processor, or how a charge pump works has been all worked out for us and is hidden from the design.

Processor Option 2

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The Microchip PIC32MX110F016B.

I went to Microchip’s website and worked through their parametric search tools.  I was looking for a device that could use the SPI interface at at least 10 Mbps and at the lowest cost.  There were no 8 bit parts that could meet the SPI requirement.  There were some 16 bit parts that could meet this requirement, but they were the high end parts.  I had to look into the datasheets to see the maximum SPI baud rate.  Since JTAG does not have 8 bit fixed width registers, I will probably have to play some tricks to use the standard SPI for JTAG operation.

Microchip PIC32MX110F016B

Device advantages

  • Two Fast SPI channels (1 for programming, 1 for data storage)
  • DMA transfers for each SPI channel– Frees software up to do data manipulation tasks
  • 5 V tolerant pins
  • I am familiar with Microchip and their IDE — MPLAB X
  • US $1.73 each in quantities of 100
  • Compatible upgrade path if this chip isn’t enough
  • Low pin count — 28 pins
  • Dip Part for prototyping

Device Disadvantages

  • I am unfamiliar with microchip 32 bit architecture
  • Limitations on free C compiler — mostly in optimization

 

Radio Option 3

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The HC05 Bluetooth Module is another possible candidate for the radio system.

It has a potential of 1.3Mb/s transfer rate.  It is priced at US$5 in singles.  It uses bluetooth serial port profile. It doesn’t appear to have FCC certification. It would come programmed from manufacturer.

Advantages to the design:

  • Easy to use
  • Low Cost
  • good speed

Disadvantages to the design:

  • Lack of FCC certification could force a redesign.

The FCC problem is too big, this radio is removed from the possibilities.