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Archive for the ‘Electronics’ Category

A slightly less yellow submarine

Posted by aonomus on November 20, 2010

So, because of the sheer expense of 6″ sch80 pipe and pipe fittings (read:  several hundred dollars for a few feet of pipe and 6 fittings!), there has been a redesign!

Posted in Robotics, ROV | Leave a Comment »

A yellow submarine

Posted by aonomus on November 12, 2010

So besides the obvious song reference, I’m starting on a new long term project (as if I don’t have enough going on?). I’m going to be building a remotely operated vehicle (ROV) with a friend for fun and potential science. This has been on my list of things to do for ages, though prohibited mostly by cost. Being gainfully employed has its benefits (ie: money).

Stay tuned for more details, as the goal is to complete construction in time for summer 2011.

Key specs:

Rated depth: 100m
Rated pressure: 1.081 MPa or 156psi

sch80 PVC pipe for electronics pods, 1″ CPVC pipe for frame, and aluminum for cross-bars

Power source:
Internal sealed lead acid batteries

Modified bilge pumps

Pressure, temperature, compass, internal monitors (temperature, voltage, current consumption, [humidity/water sensor]). Video over IP camera

Control system:
Surface control computer
Onboard microcontroller with ethernet connectivity, control via tether.

Posted in Robotics, ROV | Tagged: | Leave a Comment »

Fiber coupled fluorometer

Posted by aonomus on October 21, 2010

One of my more recent projects has been tinkering with fiber optics and sensitive detectors to make a fiber coupled fluorometer. Details to come (eventually).

Posted in Chemistry, Science, Sensors | Tagged: , | Leave a Comment »

Rogowski Coil Redeux

Posted by aonomus on August 27, 2010

Way back when I was building the capacitor bank, I built a inductive current sensor called a rogowski coil so that I could have some instrumentation to see just what kind of voltage and current I was dealing with when I used my capacitor bank. Sadly I wasn’t able to get it to work.

But first a little bit of introduction, the rogowski coil is essentially an inductive current sensor similar to a current transformer, but different in that it is wound on a flexible coilform that allows temporary installation. Additionally the can be tailored to suit a wide range of currents and are ideal for short high intensity transient pulses (such as capacitive discharge). The coil itself when placed around a conductor has a voltage proportional to dI/dt, however this by itself is fairly useless since anyone carrying out an experiment wants to know I over time.

Figure 1 – Graph of data captured from Rogowski coil integrator using a Tektronix 2012B, arbitrary scaling used. Calibration unknown on current data. dV/dt smoothing by moving average over 4 data points.

In order to extract current over time from dI/dt, you must integrate the voltage. This is done using an opamp as an integrator. By itself not terribly challenging; the hard part is data capture/acquisition, and calibration. Note that because the coil itself gives dI/dt, the peak rate of change of the circuit voltage should coincide with the peak current after integration, which is a pretty good indicator of whether you have the right configuration for your integrator.

Originally I had tried to use my sound card with an integrator + buffered circuit, however with the level of AC decoupling present, terribly ineffective with a very slow response. The trick is to avoid extra AC decoupling, and simply correct for voltage offset, which in itself is a good idea, however the challenging part was compensating for the voltage offset. If you don’t correct for voltage offset using opamps, and simply AC decouple, you introduce a RC network at every junction, and blur your current waveform over a longer period of time.

Last week I set up my old original coilgun with the rogowski coil, and a DSO that I have access to and began capturing data to test a circuit, with some success. I finalized the circuit topology and laid out the remaining tasks:

  • Prototype rogowski coil integrator with attenuator, integrator, gain stage, and line driver
  • Build current shunt reference for DSO
  • Build DC amplifier to provide current waveform
  • Calibrate stepped attenuator, gain stage to match current reference
  • Build final version, calibrate, package in metal enclosure

Posted in Capacitor Bank Mk 1, Electronics, High Voltage, Sensors | Leave a Comment »

Anderson Powerpoles and DC Backup Power

Posted by aonomus on July 30, 2010

You may recall from my last post the lovely photo of a large number of sealed lead acid (SLA) batteries gifted to me. I have finally completed the battery bank wiring with a few features in mind.

Originally I had 2x 2s2p 24VDC packs, and a 2s1p 24VDC pack, which I reconfigured to 1s10p.

I started out with this set of 7.2Ah, 12VDC SLA batteries and made up spade crimp terminal to powerpole adapters to allow for easy daisy-chaining of the batteries. I did this for a three reasons.

  • Versatility – I can split off 1, 2, 3, 4 batteries to go power some other device without worrying about disassembling a static installation. Additionally I can change the physical arrangement of the batteries themselves (rectangle, single long string, over/under, etc.
  • Compatibility – all my gear is fit with Powerpoles already
  • Safety – I can make all my connections with a small capacity, then safely series them with connectors that will never allow a short (versus attempting to crimp a long dangly cable wtih 10 crimp connectors on it and connecting it carefully to ensure no shorts occur).

Related to the above 2 photos, I filmed a 2 part video on Anderson Powerpole connectors after I received my shipment from

Posted in Amateur Radio, Electronics | Tagged: | Leave a Comment »