Downloads

Here you can find the project files as well as some interesting and useful things.

Schematics

• Sensor Schematic
• Display Schematic

Firmware & Layout

• Zip archive of the most recent firmware together with the raw schematic files and the Layout. I used OrCad 16.3 for the schematics and BAE for the layout.

Inspection Instructions

... are available only in german language.

• Display

May be you need some additional models to be able to run the simulations. I soon collected some models of standard devices that are not contained in LTspice and I regularly use them. Try here:

• 1N4007 from diodes.com: You can easily integrate this model into your standard.dio. Just pack everything into one line as you see it on the other models. By the way: I used to write own models in capital letters. So I can discriminate them from predefined ones. The actual version of LTspice will not overwrite them if you update.
• BAV99 from NXP
• BCP53 from NXP
• MC34063: Unfortunately I am only allowed to offer you the .sym I have made by myself. You have to download the .sub yourself from the Onsemi Website since distribution of the model is explicitly prohibited.

Simulations are fun and you can learn much from them without fucking anything up!

Here now the simulations:

• Simulation of the switching regulator in LTspice. Note: I did not find a model of the MC34063 which accurately simulated the function of the circuit. The simulation only shows how it works. For more, the model is not good enough.
  Unfortunately the license conditions don't allow me to offer you this poor model. You have to download it yourself to use the simulation. I chose the Orcad model which worked out of the box. There are other models out there in the internet that prove even more peculiarities. None of them would survive the startup (Vcc rising from 0 V). Symptom: Ct charges up to -2 kV and the simulation hangs.
  In reality this luckily does not happen (would be a great circuit for all those Tesla- and high-voltage freaks).
  <humor>The capacitor breaks just at 1 kV causing a total disintegration of the circuit.</humor>
  The switching frequency also does not match reality. In the simulation I set a different capacitor to meet the real frequency.
  If this was my model, I surely prohibited distribution, too...
• Simulation of the constant current source as the sensor-supply.
• Simulation of the transformer. It may be unusual to simulate a circuit as 'simple' as this but it prevents bad surprises! I measured the transformer by simple means and discretely modelled the values. So you can measure the voltage drop over the copper resistance if you like to. I only did not know how to determine the coupling factor so I left it as 1.
  The resistive part can easily be determined with an Ohmmeter. The transformation ratio I measured free running as primary to secondary voltage ratio. For the primary inductance I connected a 1 µF capacitor in parallel and measured the resonant frequency with the scope. These values may not be very accurate (e.g. inductance is not constant but is a function of the current flowing), the simulation though represents reality quite good.
  Of course, instead of a discrete simulation, you could pack the model into a quadrupole for usage in other simulations.
• Simulation of the analog output. R1 and C1 together with the PWM-output form the usual DAC, U1 takes the function of a voltage controlled current source. L1 and R2 stand for the moving coil meter. Since the TLC272 does not have a rail-to-rail output we cannot use the full voltage range. D1 provides a voltage drop to allow a current near 0 µA. R3 determines the full scale range so 100 µA will be reached at 2.7 V. C2 reduces oscillations of the circuitry.
  Here another interesting simulation. The RC-DAC has been replaced by a voltage source to speed up the simulation. It shows that especially at 0 V the leakage current through the meter allows displaying 0 µA quite well unless the diode gets hotter than 60°C since the diode leakage current is mostly soaked up by R4. R4 thereby dissipates 28 times the power of the instrument does but we are talking of less than 7.8 mW.

Once again I must state, I made the circuit and simulations to the best of my knowledge and they perfectly worked for me. I hope the information on my site are useful for you but I cannot be made responsible for their usage, neither in general nor in a special case. If you use them, it is at your responsibility and at your own risk.

5x7 LCD-Font

abcdefghijklmnopqrstuvwxyz
ABCDEFGHIJKLMNOPQRSTUVWXYZ

Well, not really part of the project but I would like to mention that the font I used here to visualize the display is freely available as a webfont or as ttf. Have a look at my HTML- und Java­script Page to learn more.