Камрад
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Вот уменьшенные картинки педалей и описание. Железяка, cтоящая рядом с педалями - это настоящий суппорт с тормозными цилиндрами.
2001-05-02
This is a short desсription for the pressure sensitive brake pedal. I wish that I had documented my work better when I was working with it, as all I have now is a bunch of notes that I hardly remember anything from.
The problem with the gameport is that it can only measure current but not voltage. I works good with ordinary resistors but when you try to connect a pressure transducer that outputs for example 0 - 5 volt, then the gameport will not be able to take any readings from it. The transducer won't even be detected at all in Windows.
That is why we need an small circuit (BrakePedalOnly.jpg) between the transducer and the gameport, to convert the voltage signals to current so the gameport can read it. The circuit will also "calibrate" the signals so we can use the full range of the gameport counts. The transducer I use outputs 0.5-1.5 volts at 0-20 bar. So 0.5 volt must give 0 mA and 1.5 volt must give the same current as a 100kOhm resistor to the gameport. This will vary between different gameports, and this circuit I have is built for a PDPI gameport. Using another gameport will require different resistors to adjust the gain and zero level. The key part in the circuit are the two PnP transistors (Q1,Q2) that converts a ~ 0-5 voltage to current signals that are about the same as a 100k pot. I did find this info on the Internet and the text file is attached to this zip-file.
Other parts in the circuit with the operational amplifier (U1:A) and surrounding resistors (R1-R3,RV1,RV2) adjusts the 0.5-1.5 Volt output from the pressure transducer to an 0-5 Volt (roughly) to feed the voltage-current converter. The variable resistor, RV1, is only calibrated once when the circuit is built to bring down the 0.5 volt output to 0 volt (at zero pressure). The second variable resistor RV2 is controlling the overall amplifying in the circuit to get 5 volt to the voltage-current converter. I have put a little knob on this one so I can adjust the required pedal pressure needed to get full brake power in games. No re-calibrating is needed in games/windows to use this knob.
The biggest problem can be to find a suitable pressure ransducer. I was lucky to find one at my work for a fair price. The pressure transducer I use is taken from a rear wheel steering system mounted on some Mercedes-Benz trucks. I think you can order it at any Mercedes-Benz dealer, part no A010 542 20 17. It can handle at least 200 bar, witch is more that enough since I only reach about 60 bar when I press the brake pedal really hard. The master cylinder is a Girling with diam .625in and the four pot caliper is taken from a Volvo 240. I tried to find the biggest caliper as I could to get the brakepedal to flex a bit.
I was at first worried a bit about how the transducer would handle the brake fluid, but that proved to be no problems since that there is a stainless steel membrane welded at the top of it to seal it.
This is my first attempt to design a circuit by my self and I am happy with it. But I had to make many different versions before I ended at this one, and I am sure it is possible to improve it. As I mentioned earlier do I use the PDPI gamecard, as I think the output from an ordinary gameport to games will be unlinear with this design.
Mauritz Lindqvist
Norrkoping, Sweden
Изменено: Freddie, 27-05-2003 в 14:41
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Потому как можно гонять даже на модеме.
