So, rev 2 was implemented...? What's going on now...?
There was a fairly significant design flaw in the first rev of the Serial NVM boards regarding the manner in which the chip select (CS) signals were asserted by the MCP23S08 IO expander chip. This design flaw came to light after I took a mental "break" from the project while waiting for the boards to arrive in the mail from OSH Park. The issue was realized literally as I was opening the mail pouch.
So, rev 2 was implemented...? What's going on now...?
About a month ago I got an unsolicited email from someone asking if it would be okay to highlight my website as the "website of the day" on their website. Initially I thought it was a joke or scam of some sort, but in fact it wasn't, and not only was it not a joke or a scam, the website requesting permission to highlight my own was none other than EEWeb, a mainstream engineering science and technology internet resource. Thank you EEWeb!
The order for the rev 2 Serial NVM Boards is officially in. I hope to have these new boards by December. Still kicking myself for overlooking the communication protocol issue (e.g. chip select). But with the changes I was able to slightly shrink the board, removing several pullup resistors and adding 3 new parts to correct the chip select issue.
I just finished the rev 2 board layout for the Serial-interface NVM Expansion Board with the added hardware to properly assert the CS lines in a mutually exclusive manner. I was also able to slightly reduce the overall size to 1.0" x 2.0". These will get submitted to OSH Park in the next day or two, or as soon as I have time to generate gerbers and carefully review them - a must unless you like spending your money on PCB's that will only get used for wall art. As I mentioned in a previous post, sample firmware development as begun and I hope to have this available soon to share. I also have plans to repackage this board into an Arduino form factor once all functionality is proven out. Stay tuned...
A while back I posted about these boards being put in for order through OSH Park. Well, I am happy to say the rev1 boards came in today; however, with much to my dismay I am afraid there is a fatal design flaw with the SPI configurations of this board... Nothing that would render this first batch *completely* useless, but in my mind this defect might as well make them useless. Maybe it's just my expectation of perfection, especially with fairly simple designs as this. As do most people, I also make design errors from time to time, but I do take pride in getting things right the first time, which this time I did not - waaa waaaa :( What I realized as I was preparing to solder components onto the first SPI flash board was this: in order to stop the write process to the NVM, the CS line must be released. In order to release the CS line to the NVM chip, two bytes must be sent to the MCP23S08 chip to de-assert the output line to that NVM chip. Well, the NVM chip will receive these two bytes and commit them to memory in the process of de-asserting the NVM chip CS line, as this output from the MCP23S08 will still be asserted until latching the 8th bit of the second byte and the MCU releases the CS line to the MCP23S08. Again, waaa waaaa :( Looks like I'll be sending Laen @OSH Park more business in the near future...
KiCAD has pretty much been the exclusive EDA tool I use for home projects and have even used it professionally. It took a little bit to learn some of the nuances of KiCAD, but overall, it's a great EDA tool. There have been a few articles about KiCAD vs Cadsoft's Eagle CAD and I hope soon to write my own comparison and also reference these other articles:
Regardless, the topic of this posting is how to create irregular board outlines in KiCAD. This is sometimes needed when you are designing a PCB for an enclosure that may have a curved profile, or other unavoidable mechanical features for which one must design.
I've been working on a few new boards, mostly for my own tinkering, one of which is this Serial-interface EEPROM Board. It's a dual-interface - SPI and I2C - board that can be populated on the TOP side for SPI hardware or populate the bottom side for I2C hardware.
I plan to build one of each flavor of this board. For the SPI side, there are many SPI EEPROM chips available in SOIC8 packages. For the SPI side of this board, I intend to use the M95M02 from ST Micro, which holds 2-Mbit each. There is room for (8) of these EEPROM chips on this board, as well as a 3:8 SPI-interface decoder. The decoder allows for true 4-wire SPI interface to the entire array of EEPROM memory. This also makes things nice from a firmware and microcontroller IO perspective.
I found this monocolor dot-matrix LCD laying in the "LCD" parts bin on my electronics bench and it sparked my interest to just do something with it. What exactly should I do? I didn't know yet.
I purchased this display for about $10 as I recall, about 2 years ago from NGX Technologies and never did one project with it until now. So maybe resurrection isn't the proper term...
Garage door safety beam as a bedroom Intrusion detection system (IDS)
It has been a while since I have had any activity on my blog, so I took this most recent experience as an opportunity to post a brief write up.
As I've been trying to get my son more interested in electronics tinkering and showing him all the fun and cool things that can be created, I suggested how cool it would be to build an alarm for his bedroom door so he knows if someone has trespassed into his room! With that, he was in....
It's been a while since I posted on my blog, so I just wanted to send a shout that I'm still alive, but have just been very busy. Between my new job position, two kids starting baseball season, a one-year-old and trying to keep up with the usual household "Mr. Fix-it" duties, I've had my hands full.
When I started this website last winter I had great things planned, but spring has come and unfortunately the site & blog have taken the back burner. So, hopefully I'll return soon for some more technical posts and to finish the posts that are currently in progress - 1) a comparison of Eagle vs KiCAD, and 2) some great embedded microcontroller resources for folks who are just getting their feet wet with mi.