Theatronics

I was taught the basics by my father, When I was young (8 or 9) he had a Ham Radio rig. I started with Tubes and my first active device project was a triode AM radio. It was basicly a crystal radio with a triode acting as a amplifer to drive a speaker. As I remember, it was not all that loud but it glowed and made noise, how much more could a kid ask for? -Mike

Indulis, You are correct, the fixed frequency method works because of the inductance, or more correctly, the impedance, of the whole motor. At a low frequency, Lets say 0hz – DC, the motor sees the full power as current through the windings and thus produces a magnetic field resulting in motion. As the frequency rises the coils begin to interact with the power in the current and some of that current is blocked resulting is losses through heating. As the frequency changes there are nodes (harmonics) that will produce better or worse power but they are not wide enough to use for accurate control. While Frequency COULD be used to control the power the motor generates it is not efficient as the full power of the supply is tapped and depending on the frequency, much of it could be lost to heating the coils. Now on AC systems there is a whole different system. When the motor is an inductive armature frequency IS the best way to control it. PWM switching is very noisy on AC circuits as the switching usually takes place using an SCR and the resulting RF noise from the sudden switch on in the middle of a cycle causing energy loss and other issues. While IGBTs and BJT’s can be used to switch more slowly, they tend to heat up and can not carry as much load as an equal SCR. The devices used are called VFD’ (Variable Frequency Drives) these drives manipulate the AC signal of 1,2, and 3 phase power to control AC motors. The phased outputs are changes in frequency and thus the magnetic fields on the armature rotate faster. Most drives range from 0 – 400hz. I have several of these drives that control 30 to 50 hp 3 phase motors. To watch one of those things speed up and slow down like a servo motor is quite impressive. In fact, given the right motor design and VFD, you can even drive them backwards by flipping 2 out of 3 phases. Stepper motors are also frequency dependant. The chips we are talking about are mostly used to drive stepper motors. Of course stepper motors do not use PWM to control speed, but rather a series of on and off signals on 3-6 channels that are repeated at a regular interval. If you had a chip that generated the drive signals for the steeper with each pulse, it could be said that the speed of the motor is frequency driven but not the power. In general, for Brushed, Perm Magnet, DC motors. PWM is the best method for both power control. -Mike

Tkjaz, Looks to be about $3.00 us. Digikey Link: http://dkc3.digikey.com/PDF/T063/1898.pdf Might be able to find them cheaper from other sources. -Mike

Check out a product called Q-Prox http://www.qprox.com/products/touch.php Sensors can pick up finger touches through thick plexy. Edge light your plexy and etch symbols into it for a amazing display/ control panel! -Mike

it's just a speaker. Usually 8 Ohms and less than a watt. here is a typical one : http://www.mycableshop.com/sku/PCCASESPEAKER.htm If you want to mount it outside just extend the red and black wires outside the case. But speakers sound louder if they are mounted in a box so you might want to put the speaker in a box. For all that trouble why not look into a nice cheap sound card? Much better sound quality and much easier to connect to external speakers. Here is a link that shows how to use a real sound card with QBasic. http://www.phys.uu.nl/~bergmann/soundblaster.html -Mike

If you want a "Way Cool" challenge. Connect a row of SMT leds on a stick and spin it. Then using accurate timing, draw the next number in mid air. (Put one digit on the left of center and the other on right of center) Hows that for wizzy bang ? -Mike

It's inside. Open up the box, you will see it. From Q-basic, I don't think so. The external speakers are usually run off a sound card, the internal speaker was rarely connected to an external jack. You can do that if you wish, just don't use amplified speakers unless you knock the voltage on the output down some (See Voltage Divider Resistors for more info) Also, don't connect a speaker larger than the one in the box as you can blow the little amp that drives it and that could be bad also. -Mike

how big of a TFT display? Are you talking about a little 2 line by 16 char type of a larger Computer flat screen type? And how large is the 7 Segment display? I guess it comes down to what you are trying to prove. If you want to show that you can build the circuit then skip the TFT and just use the 7 Segment displays. For larger displays look into “Flip-Dot” displays. They don’t need as much power as large LED signs. If you want to show off and display the output on video then you are talking about something entirely different, the whole counter BCD circuit is insignificant to the video interface and TFT driver circuit, that is assuming you want to build the whole thing from scratch.. There is a device called a “BOB-II” that converts serial data into graphics for TV sets. You might be interested in that. Then just use off the shelf flat screen TV sets for the displays. (LCD or Plasma are most common, that’s why I was wondering about the size of the TFT display you wanted to use) More details gets you more answers. -Mike

OH! I think I get it. He wants to put the scope into the X-Y mode (Ch1 on X ch2 onY) and use the PIC to control the signals to DRAW a game on the screen. If it's a 30Mhz it must be a fair machine so I am guessing it also has a Z input on the back that can be used to control the intensity of the beam. I have seen people build driver circuits and display NTSC signals on a scope screen before. It wasn't easy but they were trying to comply with a broadcast signal. This may be easier because he can control the whole thing. Humm. I’d suggest ‘Vector’ graphics rather than trying to scan the whole screen. These are very similar to an etch a sketch with an on off button. You will need a pair of fast D-A converters. If you load a specific X,Y value into the converters and the send that to the scope and wait just a moment for the screen to settle you will illuminate a DOT on the screen BY sending a series of locations to the system you can draw anything. So rather than keeping track of thousands of pixels, just keep track of the actual dots you are using. In the game world they are called sprites. A sprite is made up of a collection of pixels relative to a single origin. Usually the upper left corner. A sprite might look like this for a square 0,0 1,0 2,0 2,1 2,2 1,2 0,2 0,1 If I pick a point, (25,10) for instance, and plot my sprite there it would be (25 + 0 , 10 + 0) (25 + 1 , 10 + 0) (25 + 2 , 10 + 0) (25 + 2 , 10 + 1) (25 + 2 , 10 + 2) (25 + 1 , 10 + 2) (25 + 0 , 10 + 2) (25 + 0 , 10 + 1) So you would need to create a sub for each sprite If we create one for “SQUARE” We would pass it the X,Y location of the square and it would plot a square where ever We tell it too. You might need some subs like (Tank1,Tank2,Bullet1,Bullet2,Tree,Rock,House) Then by allowing game play to determine the location of each item you simply call the subs with the correct X,Y locations to draw each item. (* Note Drawing an item would be sending the voltages of Vx + sp and Vy + sp to the scope while the beam is on and then turning it off when done) If the subs are called at a regular interval there should not be too much flickering with a 20mhz PIC. I’d set the subs up with an interrupt to refresh the sprites every 1/20th of a second. (About the speed of the human eye) You might want to tear apart a joystick and see how to wire one or 2 into the Pic. You will need 5 pins for each one (Left, Right, Forward, Backward, Fire) Is that what you are looking for? -Mike

The 556 chip is very similar to a pair of 555 timers. On the left side of the chip the Cap and resistors are used to set a frequency for the signal. Usually this frequency is not needed to be exact. Most servos are forgiving but it should be around three thousand pulses per a second or 3 Khz. Use the adjustable resistor to move up and down the range until your servo starts to respond. The Cap and resistors on the right ser the Pulse width. While the left side of the 556 is acting like a simple pulse generator, this side is wired as a “One-shot” with every pulse that the left side creates , the right side generates a pulse whose length is determined by the capacitor and resistors. The switch at the top of the circuit shorts out the 10K resistor. When the switch is open the resistance is such that the pulses generated are much longer and this causes the servo to turn all the way one direction. When the switch is closed, the 10K resistor is effectively ‘taken out’ of the circuit. With a lower resistance the pulses now become smaller and the servo changes direction. There are 2 “extra” capacitors in the circuit. On pins 3 and 11. these are needed to keep the circuit stable. While they do play a role in how the circuit works, if you are a beginner, focus more on the resistors and capacitors on the outside edges of the circuit. Good Luck! (PS. Some servos are designed for speed, others are made for power. The more powerful ones are usually slower also. If you want your doors to ‘slowly’ open you can use a high torque/low speed servo. The other way to accomplish the speed control is to alter the speed that the resistance of the 10K resistor is changed. This is a bit more complex but you might enjoy the challenge of figuring it out.) -Mike

Try using a (MosFet N-Channel Enhancement mode) to actually switch the LEDs on and off. Many fets can be connected directly to a microcontroller. (NOT all, check your datasheet) For 50 of them, There may be a PIC that has 44 I/O pins but I'd suggest a different method. Look into "Serial In / Parallel Out" Shift Registers. You can string them together end to end. There is a Serial in pin and a serial Out pin and then (usually) 4 or 8 output pins. There is also a /Latch/ or /Load/ pin. Then by placing the on and off signals on a data line and pulsing a second line to provide a clock signal, you can load all 50 bits in 50 clock pulses. Then just send one more pulse to the /Latch/ pins and all 50 bits will load into the registers at the same time. Tie a logic driven MosFet to each output and you can drive nearly any load. With a system like this you can create a single board that has 8 drivers on it and then replicate that board 8 times to get 64 outputs. The PIC doesn't care, it just sends out 65 bits and 64 clock pulses followed by a latch signal. Many Pinball games and Slot machines operate all the lights and some of the playfield systems using this method. -Mike

Zoinks, that’s a lot of questions. All right 1 at a time: Touch sensors. A FET touch sensor is the same thing used on those lamps that you touch to change the brightness. IT can be done with any high gain amp. If you have ever touched the input to an audio system and heard that loud hum noise, you know how it works. The input is sensitive and can pick up the touch of a person. But rather than drive an audio signal it just flips a relay. Another touch type switch is called the Q-Prox. It is a single chip solution that uses a simple wire coil to detect a touch. I have included a link to the part. They have other chips that offer multiple inputs (2 keys,4 keys ect) http://www.qprox.com/products/qt100.php On the issue of Reversing the Servo. I guess I would need to know how you are making it go forward in the first place. While this is not the normal usage I have seen a very simple application of R/C Servos where the Power and ground leads were connected and the signal (White or yellow) wire was simply connected to +V to rotate the servo to full right and ground to move it full left. The servo normally looks for a 1.5ms pulse every 100ms (max) to maintain a position of

Paul_J, That’s like the test I was talking about. We did it (2 decades ago) in a class on microprocessors of all things! It was just a side note where the instructor demonstrated how heat sinks have different abilities. He used the Soldering iron as a fixed and constant heat source. But he just glossed over the calculations he used. I do remember now that the goal was to get the whole heat sink to the same temp. A better heat sink Would maintain a lower temp than a poor one given the same energy input. Indilus, Huh? I thought copper was about 2 times better than aluminum so for the exact given shape and size? Diamond (2300 W/mK) Pyrolytic Graphite (1950 W/mK) Silver (429 W/mK) Pure Copper (401 W/mK) Pure Aluminum (237 W/mK). Of course that is only true of pure metals, Alloys are generally much lower than any pure metal. So a pure aluminum sink could be the same as a low grade copper sink. But it is very rare to find affordable copper sinks any more. So I guess the whole thing is moot. I have used copper water pipe before. Flatten out one end, Drill a hole to mount the part and then split the sides of the remaining tube open . In a pinch it works fine. Speaking of water pipe… Has anyone mentioned water blocks yet? -Mike

What type of metal is important. (Al is most common) Also the shape is important to some degree. If the part is mounted at one end of a long sink the wattage will be lower than if the part were mounted in the middle of the same sink. I don't know of any actual 'formula' to convert the shape, material, and surface area of a sink into an actual wattage or Efficiency % value.

When you say Miniature, I assume that you mean smaller than human sized? If that is true, the sensors depend on what you expect to ‘trigger’ the doors to open. The classics are: Photo transistor: When exposed to light it will conduct. By covering it (making it dark) it will conduct much less. Cds Cell: Similar behavior, Acts like a resistor that is sensitive to light. Hall effect sensors. If the item being sensed is metal (Fe) based. Fet-Touch sensors: Very high gain sensors that detect the static discharge of human touch. Capacitive sensors: Good for sensing just about anything except they have a very limited range. (usually millimeters) Some other devices that MAY NOT be useful due to the model being ‘miniature’ Ultrasonic: I have not seen a micro-Ultrasonic setup but I suppose it could be done. I think the trick would be building a pickup that can detect the weaker ‘clicks’ PIR (passive Infrared) This usually only works on Living/Warm blooded things. It is the same concept as the Photo transistor except it detects HEAT from a body. Some are so sensitive they can detect changes in air temp but usually only over a large area. It could work but it would be difficult to use in a very small area. Pressure mats: These are often expensive if you buy them but I have seen very functional ones built from foil and paper. They normally require at least 50lbs to trigger. Let us know more about the size of the model and what will trigger the doors and I am sure someone will have a clever idea to help. -Mike