An order from RS delivered today with parts for a ColorHug, a device for color-calibrating your monitor.
The circuit is based on the TCS3200D color-sensor which RS had on their website when I made the order, but the delivery note lists the parts as "discontinued". So these have to be sourced from somewhere else.
My legs aren't exactly recovered from Saturday's marathon, but a slow 5k jog anyway today. Sports Tracker was released for the N9 last week (or was it earlier?), so I thought I'd do some GPS testing. Held Garmin Edge 800 in my right hand and the N9 in my left. The results aren't that great for the N9:
I should do a test on the bike later. Maybe include the Garmin 405cx and older C7 phone also?
The touch-screens on these devices are different: Edge 800 works fine with gloves, N9 doesn't work at all with gloves.
Cropped from original like this:
#!/bin/sh mencoder video.mp4 -oac pcm -o test.avi -ovc lavc -lavcopts vcodec=msmpeg4v2:vpass=1:vbitrate=5160000 -vf crop=370:300:200:100 |
I made two small circuits today for temperature control of the extruder head on a reprap type 3D printer. The idea is to control the temperature, which needs to be somewhere between 200 and 240 C I think, using EMC2 and two parallel port pins.
The first circuit is based on the 555 and produces a square waveform with variable frequency depending on the resistance of a thermistor. At room temperature the thermistor resistance is 100 kOhms and the output frequency is below 1 Hz, and when the temperature is suitable for extrusion the thermistor resistance is about 200 Ohms which produces an output frequency of around 25-30 Hz. If the EMC2 base-thread runs with a 50 us period then it should be possible to record the frequency of this square wave using an input pin on the parallel port with an accuracy of roughly 1/500 (half a degree C?), which should suffice.
Testing the heating side of things, a wire with about 6 ohms of resistance wrapped around the extruding head, showed that a suitable DC voltage is around 8 V and produces a current of 1.3 A. The idea is to use a HAL PWM-generator to drive the base of a 337 transistor which drives the gate of an IRF610 FET that controls the current through the heating wire. By adjusting the PWM duty cycle it should be possible to control the temperature using a PID controller based on the temperature measurement.
We have a 1994 LPKF Protomat S91 PCB mill in the lab for making prototype PCBs. Here it was used to cut a circular part (not a PCB) which was first drawn in CorelDraw, then saved in HPGL format, and then opened in BoardMaster which is the program that controls the mill through a quirky serial protocol. I think the original LPKF design has a solenoid for the up/down z-movement of the tool. The solenoid would become unreliable during a long run, because it was getting very hot, so on our mill it has been replaced with a more reliable pneumatic cylinder. The spindle is a Proxxon hand-tool, and tool changes are manual.
Gone is the HiTec light-blue box, and replaced with a clear one. These servos, which HiTec calls "monster torque" 🙂 are designed for either 6.0V or a LiPo pack at 7.4V. They are about 10% bigger than the standard 20x40 mm footprint, and produce 36 kg*cm (6.0V) or 44 kg*cm (7.4V) of torque. To be tried as a winch servo in the prototype PIKANTO.
The heating elements on this heater just kept on heating and heating independent of the temperature. I first checked the thermocouple that measures temperature - but that seemed OK, so the next thing I suspected was the solid-state relay that turns on/off the heating. Turns out this initial guess was right, and I was lucky we had a replacement on the shelf, so now the heater works again. The picture above shows the broken SSR on the right.
New SSR in place.
Verkkokauppa.com:s 199 euro offer for a 2-year-old refurbished Thinkpad T40p proved irresistible, and I was lucky to pick one up after queuing outside for 35 minutes. The place opens at 9, I arrived around 8:55, but some people had apparently been outside the doors waiting already at 7:30! The 19 euro mobile phones sold out before I made it inside.
A quick look inside, tightening some loose bolts, and dusting it off with compressed air. Should make a nice second laptop (autoguiding for astrophotography, chart-plotter on a boat, or similar)
I used this Sallen-Key design to build an 8-channel 4th order low-pass anti-alias filter for a 16-bit 200 kS/s +/- 10 V AD-Converter. I calculated the components for the 60 kHz low-pass Butterworth design with this on-line calculator. Previously I've used the MAX274, but that component is limited to +/- 5 V signals. Here I really need the +/- 10 V voltage swing. The exact design calls for 2872 pF, 2452 pF, 6935 pF, and 1016 pF capacitors, but I looked at the transfer function with what values were available in 1% tolerance from Farnell, and the response looked fine with (R= 1 k, C1=C2= 2700 pF for the first stage and C1=6800 pF, C2=1000 pF for the second stage). Both the resistors and capacitors (~1.5 eur/pcs!) have a tolerance of 1 %, which according to a monte-carlo simulation should not affect the response that much. I'm using OP42 op-amps with a unity-gain bandwidth of 10 MHz, which should be adequate (100x the cut-off frequency was recommended in a guide I read, that would be 6 MHz in this case).
For testing I hooked up a signal generator and an oscilloscope and wrote a LabVIEW program to loop trough around 250 different frequencies while recording the peak-to-peak value of the filter input and output signals. The oscilloscope only has an 8-bit AD converter, but I adjusted the analogue gain between 5 V/div and 2 mV/div to achieve effectively around 16-bit dynamic range.
This is the result of testing all channels with a 20 Vpp sine wave between 100 Hz and 10 MHz. The blue curve shows the design response and the red and green curves show the maximum and minimum expected response from the monte-carlo simulation (I drew all component values from normal distributions with 1 % standard deviations). Pretty nice agreement until ~500 kHz. Here's another view of the data:
This figure shows the deviation of the real filters from the design response, again confirming that everything works as it should up to 500 kHz.
Log-log plots can be confusing, so here's a semilog plot and a linear plot of the same data:
Here are the source files for this design:
The box actually looks like this.
