What are you building?

Today i assemble a Velleman k8065 pocket tone generator. I am betting other people are doing better projects. So are you doing better projects which ones would you like to show off?


3lb Core Burn Black Powder Rocket. Shot it off on the test stand to check thrust and burn duration. Peaked at 70lbs of thrust with a curve from 40lbs to peak over about .5 seconds. This is one hot rod of a motor. Put up a 3 inch salute ball shell, lifted it like it wasn’t even there! Love making rockets.
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A bit of SMT oragami with a LTC1615 boost converter for a small solar power experiment.


I had to fix a poorly repaired Trog arcade game board… where someone used magnet wire and silicone to patch traces.

Since it was giving errors on the custom chip at U99 and I had to check ALL of it’s connections, and since the schematic only showed bus connections, I pinned out the entire custom PGA chip. I’m surprised nobody has done it before - I looked and searched and Googled…

…then spent an hour tracing and documenting a 144 pin PGA chip.


I’m building a flow and pressure sensor for open-source ventilators. It’s the one part that so far all open-source designs haven’t touched, yet it’s perhaps the one most important part that makes the difference between a helpful ventilator versus a homicidal ventilator.

It was broken out of the COSV project and modularized as the VISP project upon realizing that all ventilators need it yet none so far have it.

The novel aspect of this approach is that it uses absolute pressure sensors, which have high global availability, instead of differential pressure sensors, which are what commercial ventilators use but they have very poor instantaneous availability and that’s a serious and under-discussed problem given that we need at least a million new ventilators within just a few months.


Can you use any of these?


I have a stick and a half of them, NOS, SenSym brand.


Thanks. We have enough BMP280 for a few tens of prototypes and for now we’re still needing to prove whether absolute sensors can even stay calibrated well enough to work for a pitot tube which is technically a differential application. I’m expecting a problem with absolute drift over time between sensors and hoping it won’t be as bad as it could be. No one specifies that in the datasheet so we can only find out empirically.

I’m wondering though if the world is actually going to end up needing multiple designs that each use different sensors in case one manufacturer just isn’t able to make enough sensors in time. The pressure sensor is definitely the bottleneck part. I’m still waiting to hear from Bosch on a lead time for 200,000 units but I went with BMP280 for now because they already have tens of thousands in stock distributed around the world and there are at least two other parts that fit the same footprint including a (gasp) chinese clone that happens to have high availability.


Cool. These are just sitting here and I’m just trying to find a home for them rather than throw them away.

They came from a closed shop in Richardson that made dive computers for the Navy SEALs.


You are really on top of it with the good selection for the flow control. Some engineers in the media had mentioned the lack of engineers with the for sight to see the real need for flow control in respirators. Are you working on other things?