Level Shifting and Tablet Building …

circuitfloor1Figure 1: The new tablet uses re-purposed materials on the circuit board floor.

This project is more involved than a simple exercise in converting 3.3 and 1.8 volt logic levels.  It also involves building yet another homemade tablet.  I have four of them now (2 Pi2’s, a C1, and a C1+).  The fifth one (being this XU4) will be the most powerful of the bunch.  So, in figure two we can see I’m beginning to lay out the new tablet…

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Homebrewing a Board for the MCP3426 ADC


Figure 1The simple connection from the USBIO to the ADC

The ADC devices currently in all three of my “homemade” tablets are a little under powered, so we’re upgrading all of them to use 16 bit Microchip MCP3426 ADC chips. The smallest reasonably hand solderable chip package is the SOIC. Most of the newest, fastest most glam chips are not even available with old-time DIP packages anymore. This is seriously bad news for oldish guys like myself.

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A Digital Compass for the Homemade Tablet

compass-adafruitBFigure 1: The digital compass has been mounted in the original homemade tablet, next to the powerful Imedion NiMH “C” cell bank.

The next item to be added to the original homemade tablet was a mims/magnetic compass (purchased from Adafruit at Adafruit.com).  It is an i2c device, so is only a four wire connection (Vcc, Gnd, SCL, and SDA)…

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crammed-raspiriscytabletFigure 1: The “homemade tablet” is getting cramped. (Click to expand)

In figure 2, it can be seen that the little “homemade” tablet is getting quite cramped. Note that I did not mount the Cirrus card on the 40 pin IO connector of the Pi/2. This was to facilitate use of the GPIO pins for other things. There is also a vertical clearance problem to deal with. So, there will be individual wired female header lines coming from the audio board to the Pi/2 J8 connector (not yet in place).

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Rehab for the second “Homemade” Tablet

Recently, I decided to give the engine inside the latest “homemade” tablet project a rehab.  I decided to add an internal battery supply, but to make it a decidedly different kind of thing this time around.  As with the first homemade tablet, this one is geared to use NiMH batteries (I love those things!)  But – I intend to do the battery charging operation in a different manner than was done in the first tablet. I sometimes call the second “homemade” tablet the “Raspi-Riscy” – to differentiate it from an earlier homemade tablet based on the Odroid/C1.  The latest homemade tablet project uses the Pi2 SoC/SBC board.  Initially, I installed the RISC OS operating system onto it.

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Note: This author and site is not affiliated with the Raspberry Pi or the RISC OS operating system in any way.  For information, see https://www.riscosopen.org and https://www.raspberrypi.org.  The Odroid C1 is a product made by Hardkernel at hardkernel.com  This author is not affiliated with Hardkernel in any way.

A “Homemade” Tablet that uses the Pi2

recessed_switch-3 Figure 1: Recessed switches on the enclosure containing the tiny display and the Pi2 SoC based SBC might be an effective anti-bump device.

Posted 01/18/2016:

Recently, I picked up a Raspberry Pi2, just to see what all the excitement was about. I ran it through its paces, putting some of my favorite obscure operating systems on it (standard practice for me, when dealing with new SBC devices). The Pi2 successfully ran FreeBSD, NAS4Free, Raspbian, and RISC OS. (Granted, Raspbian is not an obscure OS).  My favorite of these, at least on the Raspberry, is RISC OS. It’s the OS that gives me the best impression of speed, although that is a feeling based only on the responsiveness of the GUI.  Since RISC OS uses only one core, it’s not going to process “R” statistical package weather forecasting data faster than the Raspbian.  That’s not a problem – and perception counts when all you really want to do is read the headlines in the news with Netsurf!

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The Homemade Tablet’s Little Brother

serverodroidwithbattery1 Figure 1: We’re growing the family, and HT version two is being born. Here it is shown, perched on top of the original “homemade tablet” (click to enlarge).

Originally, the idea was to put a very small display on the panel of this Hammond aluminum enclosure. I’ve changed plans, and it will just be a server droid.

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Homemade Tablet – Fun with Auxiliary batteries

eightcell6Figure 1: Working up a new battery configuration.

The new batteries arrived in a small but heavy package. I pulled the brand new Imedions out of the box, and tested them for voltage. All but one was OK out-of-box with no further charging needed. For the one, fortunately, I had kept a pre-charged spare in the battery drawer, to round out the eight battery line-up. Next, I pulled four dual “C” battery holders from the same small mail package, and arranged them on a piece of trim board (not something a person should normally do, but I did for this little test). The next little jewel that I pulled from the shipping container was the DC-DC (voltage, not frequency) down-converter. Not being patient enough to wait for the housing that I had ordered, that the batteries will ultimately reside within, I soldered a switch to a couple wires, pushed the batteries into place, connected the pack to the DC-DC converter, and threw the switch!

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