He sat on the edge of his cot, rifling through the papers that had been collecting in the small corner of the hooch he used as an office. Reports, maps, dossiers, printed emails… worthless — all of it. As he worked through a drawer full of folders, only glancing at one after another before adding the contents to a growing pile, he paused on a rather thin one and pulled out the few papers that were inside. These he would keep, nothing else. Setting them aside, he grabbed the rest in single motion and threw them down on the discard … Read the rest
The brown sort of desert that is Albuquerque isn’t my favorite environment. I miss trees and brush that are even slightly green, and I could happily go the rest of my life without ever running into a cholla cactus again. That said, new Mexico has it’s charms. One of them is quick access to the trails in the Sandia foothills, some of which are within a mile of my front door. The last two Saturday’s in a row, Michael and I have hiked one of them to a large granite formation that looks almost like a dam. This last Saturday, … Read the rest
I’ve finished the updated design for my TDCS controller, but I’m waiting for a few parts that I didn’t have on-hand and couldn’t strip off of the board that represented my first attempt. Rather than just sit around and wait, I decided to figure out how to make a decent set of electrodes without ordering stuff online.
I used a standard 3.2mm mono-jack to connect the leads, and had intended to build my own cables. However, I don’t have any wire around the house that is suitable for this use. All of it is either way to heavy a … Read the rest
An unfortunate outcome of many first attempts is the learning that goes along with failure. My initial design for a TDCS controller had some weaknesses (okay… outright failures). At first, I attempted to fix them on-board by cutting traces and soldering wires to re-route power, or by dead-bugging extra components onto it. However, you can only do so much without having to shift gears and start over. This post is all about the redesign.
The driving force behind the re-design was my inability to make the TSC888 current sensing amplifier work like I wanted. However, I can accomplish the same … Read the rest
In previous posts, I described the process I went through to design and fabricate a circuit designed to safely apply 1mA of current to any load (including potentially a human). Up to this point, things had gone well. The TSC888 amplifier intended to measure the actual current flowing turned out to be a little small for hand-soldering, but my practiced and patient hands managed it okay. I wouldn’t recommend it to someone who is just starting out with surface mount components though.
With the board built, I plugged in a 9V wall-wart transformer, connected a 1K resistor to substitute as … Read the rest
In the previous post, I described a circuit design for a TDCS controller I’m developing. Because I’m working almost exclusively with surface mount components, I can’t really breadboard the circuit. The best option I have is to build a circuit board and use that for testing. Conceptually, I could send the board out to a fab shop and have them produce one. However, doing a 1-off build, especially when the design hasn’t been proven, is expensive, risky, and takes a while. Because I’m impatient and like to do things myself, I make my own. In this post, I’ll describe … Read the rest
NOTE: This was an initial design, that evolved as I built and tested it. For the final design, complete with a description of each major component, see this post.
The fundamental building block for any TDCS controller is a current source capable of supplying between one and two milliamps of current through the human body. This can be a bit of a challenge because the resistance of the body varies with electrode placement, skin resistance (which can vary from one second to the next), body composition, and a bunch of other factors. The trick is to build a regulated … Read the rest
CAVEAT: The design described here has fatal flaws. I’ve since re-designed it, and have left this here as a way to document the process and share the realities associated with designing even relatively simple things with whoever might read it. The current design is available here.
I don’t seem to be able to function well without some kind of project. Usually I have several waiting patiently for my attention. However, at the moment all my current ones require either time, money, or energy I just can’t afford to give. I have a coding project to finish the user interface for … Read the rest
How often do we casually ask someone we encounter how they are? Passing a casual acquaintance in the grocery store isle, the nearly universal greeting is to ask how they’re doing. Run into an old classmate you haven’t seen in a few decades who has their arms full of kids and is clearly on their way somewhere, and we ask how they’ve been. I know I’m guilty of it, and I’m pretty sure almost everyone else is too. This kind of callous or ignorant questioning needs to stop. We don’t really want to hear about our former classmate’s recent divorce … Read the rest
Third night in a row… And too tired to use the quiet time to do anything productive.