tschum

's profile
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Assoc Elect Engr

I started in TV repair in the early 1970s, then later moved into industrial electronics (phototypesetting machine maintenance). After that I got into engineering, and in 2001 found Fibertek, a maker of lasers. This was the dream job. Now I'm semi-retired, and still learning.


tschum

's contributions
  • 11.14.2012
  • Writing a technical feature for EDN
  • I'd like to praise the editors for how well they handled my article last month. Editing was done, but was minimal, and the result was significantly better than what I submitted. There were a few emails back and forth, all of them friendly and encouraging, and they made sure that I knew when the article was published, and how to find it. This is a great way to get exposure for your ideas since hundreds of thousands of engineers (or at least hundreds) will see it.
  • 01.31.2017
  • Adrift on the meandering path of product development: DC-probe case study
  • This is a great idea! I have to try this before designing in some expensive alternatives. Thanks for suggesting it! It solves another problem as well, because without it I have to be very careful to avoid securing the knob right down against the panel. Have you thought about doing a guest blog on one of your projects? Think about it!
  • 01.31.2017
  • Adrift on the meandering path of product development: DC-probe case study
  • Thanks for taking a look! This little article just skims the surface really. There are a thousand small issues when the design hits the pavement. The console has three knobs for example, and two of them might never be used. These are the offset adjustments, and even after I found that these lines can simply float to ground in the probe board I still had to decide whether or not to support the feature. So, I go to a lot of extra trouble to provide these adjustments in the product, knowing that they will most likely never be used. There is always the one case that might come up, where the offsets will be needed... I might be guilty of overdesign here, but at least I feel better.
  • 01.31.2017
  • Adrift on the meandering path of product development: DC-probe case study
  • Film is best, as you say. My design was built for 0805 ceramics, so the easiest fix for me was to go to NP0 ceramic. This is far less microphonic than X7R, but not as good as film. In the past I've done audio and all the caps were film except for two power supply bypasses. Film is the way to go for low noise.
  • 01.31.2017
  • Adrift on the meandering path of product development: DC-probe case study
  • Yes they do, frequently in the 4gigohm resistance range at maybe 4V max. The design I did tries to reduce all forms of loading, not just input impedance. So, the probe puts about 3pF of capacitance loading and very small inductance loading into the equation. This is far better than the typical 3ft long test lead that you would use with your multimeter. The solid wire length of the probe tip is only about 2.5 inches. On the other hand you could probably put a 100 megohm series resistor at the probe end of your multimeter test lead and you could do pretty well. This would most likely reduce your capacitance and inductance loading quite a bit, and it is a whole lot easier than building my design! So, with the first comment my product becomes obsolete! Maybe I can think of a better idea soon...
  • 12.13.2016
  • Sensor conditioning amidst a sea of focus on MEMS and sensors
  • For those micropower discrete analog subsections of sensor implementations, where the usual 10 megohm input impedance of standard multimeters is a disruptive influence on what you are trying to measure, I've worked out a high impedance probe design that might be useful. See it here: http://tomschumelectronics.com/about.html