Older blog entries for Nic (starting at number 182)

15 Jul 2006 (updated 13 Aug 2009 at 18:33 UTC) »
July 14th, 2006

A couple days ago I made an encosure for the interface circuit. Over the past couple days I've been working on getting the reverse circuit to work, and today I soldered it and built an enclosure for it. This circuit's job is to prevent the car from being switched from drive to reverse or from reverse to drive while the car is in motion. If the reverse switch is switched to reverse while the car is driving, the green drive light turns off and the red illuminated reverse switch blinks on and off until either it is put back in the drive position or the car comes to a full stop. It works the same for going in drive from reverse. The circuit can tell if the car is moving by checking for a current accross the motor terminals. This board has 18 components per square inch and 72% of the perf holes are used.

There is a picture at http://www.craterfish.org/teamprodigies?pictures?2006/Jul

11 Jul 2006 (updated 13 Aug 2009 at 18:34 UTC) »
July 10th, 2006

I finished soldering the interface circuit today. This circuit has 12 connection wires total. It has two power wires, three wires for the gas pedal potentiometer, three wires for the brake pedal potentiometer, one wire for reverse, and three wires (direction, high-side power, and low-side power (PWM)) to control the four H-bridge circuits. These last three have indicator lights soldered onto the board - a red LED for direction, a green LED connected to the PWM signal, and a yellow LED for high-side power. I tested the circuit on the H-bridge circuit I've built with one of the motors and it worked great.

This is a complicated little circuit. When generating a PWM signal, it must ignore the gas pedal position if the brakes are on. In addition to generating the PWM signal, this circuit has to give the motor controller a direction signal. This signal must be forward if the gas pedal is down and the car is going forward and backwards if the gas pedal is down and the car is in reverse, but in both situations it must be inverted if the brakes are on. It uses an XNOR gate (or snore gate as I like to call it) to accomplish this. It also has an output to turn the high- side MOSFETs in the H-bridge circuits on or off. They are on whenever the brakes are off and off when the brakes are on.

This is definitely one of my more-compact circuits. It's smaller than the voltage doubler circuit. With a total component count of 56 and dimensions of 2 1/8" x 1 1/4", there are approximately 21 components per square inch, and that's not including wires. Of the 286 holes in the perf- board, 211 of them have a component lead or wire through them. That's 74% of the holes that are used. Look at the pictures (http://www.craterfish.org/teamprodigies?pictures?2006/Jul) to see what I mean.

6 Jul 2006 (updated 13 Aug 2009 at 18:36 UTC) »
July 6th, 2006

A few days ago I made a nice little enclosure for the voltage doubler circuit. It might even be water proof! There is a picture on July's progress page (http://www.craterfish.org/teamprodigies?pictures?2006/Jul). Yesterday I finished and printed out a circuit for all the vehicle's core electronics. Last count I think there were 75 transistors.

30 Jun 2006 (updated 13 Aug 2009 at 18:37 UTC) »
June 29th, 2006

I made an enclosure for the H-bridge circuit. It is sealed except for the two ends, so that air can flow through it to dissipate the heat. Now it's time to design the PWM generating circuit and forward/reverse/braking control circuit.

I posted a picture on the progress page for June: http://www.craterfish.org/teamprodigies?pictures?2006/Jun

29 Jun 2006 (updated 13 Aug 2009 at 18:38 UTC) »
June 28th, 2006

I soldered the H-Bridge circuit that I designed. I noticed a major flaw in the circuit design - I had it so that either the left MOSFETs were both on or the right MOSFETs were both on which would short out the circuit and melt stuff. Fortunately I noticed this before I soldered the circuit. The new diagram is at http://www.craterfish.org/teamprodigies?pictures?2006/Jun, along with pictures of the finished motor controller. The heatsinks are set up in such a way that the entire circuit board will go inside a tube that will have air flowing through this. I may put a fan in, or I may just have an air intake on the front of the vehicle.

The motor controller is user-proof. It has two wires for the motor, a ground wire, +12V, +24V, a direction input, high control, and low control. The high and low control wires turn the power on or off to the high-side and low- side MOSFETs. The low-side power can be controlled with PWM. The high-side MOSFETs would be turned off for regenerative breaking, while the low-side remained on with PWM.

29 Jun 2006 (updated 13 Aug 2009 at 18:39 UTC) »
June 27th, 2006

I soldered the voltage doubler circuit today. When I was designing the component layout I spaced everything out as far as I could stand. Normally I try to make everything as compact as physically possible, but usually the circuit stops working and I throw it away because I don't know what went wrong and there's no way to find out. This way hopefully nothing will go wrong in the first place, as it's very organized and well-made, and if something does, I will be able to test at points and fix a bad connection or whatever it is.

Go to June's progress page (http://www.craterfish.org/teamprodigies?pictures?2006/Jun) to see a picture of the soldered circuit-board!

28 Jun 2006 (updated 13 Aug 2009 at 18:40 UTC) »
June 26th, 2006

So it turns out the voltage doubler circuit wasn't perfect either. When the multivibrator capacitors were small (0.1MFD) for some reason it made the output stage transistors overheat. If the 47MFD capacitors were removed, they did not overheat. I imagine the problem was caused by some sort of voltage spike from the capacitor, but it only mattered at high frequencies. This may be a problem with the new circuit also. Another problem with the old circuit was that the output voltage was actually about three volts less than twice the input voltage. I haven't tested this circuit, but the new output stage should get the voltage within a fraction of a volt of twice the input voltage.

Notice the difference in the output stages between the two circuits - I switched the position of the NPN transistor and PNP transistor. The old version was fail-safe; it was impossible for both transistors to be on at once. With this system, however, I had to choose four resistors to create a voltage divider that would ensure that only one of the transistors was on at once. If the input voltage is above 15V, the voltage divider no longer does this, and both transistors will turn on which will short negative to positive and melt the transistors. The benefit of this output stage is the much larger range in voltage.

Go to http://www.craterfish.org/teamprodigies/?pictures?2006/Jun to see the new voltage doubler circuit!

28 Jun 2006 (updated 13 Aug 2009 at 18:41 UTC) »
June 25th, 2006

I did some tests on the H-bridge circuit and made several modifications. One change was to switch the NPN power driving transistors with PNP transistors which saved a couple volts. Another change was to replace the diodes from the direction input with NPN transistors. It turned out the voltage drop accross the diodes was too much to pull the bases of the transistors low. I also made the smallest amount of resistance from negative to positive in the logic part 10 kiliohms rather than 1 kiliohm to save power, which is important when using the +24V source. It's also nice to save power wherever possible on an electric vehicle, because those miliamps add up!

Go to http://www.craterfish.org/teamprodigies/?pictures?2006/Jun to see a schematic diagram of the new H- Bridge circuit!

24 Jun 2006 (updated 13 Aug 2009 at 18:42 UTC) »
June 23rd, 2006

I did some research on the internet and discovered the solution to a high-power charge pump - the push/pull driver. This is just a combination of a PNP transistor and an NPN transistor, but it allows the output of a circuit to be shorted high or low with no resistors in between, which is what I needed. I designed and built a new circuit, and it passed my tests. I posted a circuit schematic at http://www.craterfish.org/teamprodigies/?pictures?2006/Jun.

24 Jun 2006 (updated 13 Aug 2009 at 18:42 UTC) »
June 22nd, 2006

I redesigned the H-Bridge circuit. The new design is much simpler, and hopefully won't melt any more MOSFETs. I put a circuit schematic on the progress page at http://www.craterfish.org/teamprodigies/?pictures?2006/Jun. Since that voltage doubler circuit melted too, I'll have to redesign that.. and I'm realizing that the new design will have to be capable of powering a load that draws more current than just MOSFETs - in the H-Bridge circuit I designed the 24V source has to power some of the logic circuitry also. I also realized that the current draw of the last circuit was limited by a 1k resistor, so at 24V that would be a max of 24 mA. There was also a voltage drop accross the 1k resistor whenever the circuit was powering a load, which caused some problems.

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