Student needs help for high school science teacher

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macgeek10
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Student needs help for high school science teacher

Post by macgeek10 » Fri Oct 13, 2006 8:59 pm

I am currently a junior in high school and am an avid electronics buff. I am attending a tech prep program through my high school's "vocational program" for electronics, and am so eager to learn just how all of this stuff works. My main future interests as far as electronics goes are in pic and wireless control, for robotics. Our "trade school" competes in robotics competitions every year, and I really want to help out as much as I can. I took apart my first radio when I was 10 and looked at all the beautiful colored components with wonder, and really wanted to know how they all worked. Not knowing any better, I ended up prying them all out with a screwdriver :o .

My uncle, an electronics engineer who lives out in California, was in town on my 12th christmas, and purchased a whole bunch of electronics stuff for me, not the crappy radioshack stuff, nice, technician-grade tools. Just today I acid etched my first board, a pic programmer, which turned out looking great, but I really have no idea how to do pic programming yet :smile:. I have accumulated a good collection of electronics components, junk, and knowledge, but I have a dabbling of basic electronics, nothing fancy. I wish I could learn it all faster, but my teacher can only teach so fast.

I recently found out that my freshman highschool introductory physical science teacher was retiring this year, and I talked with him for a while. He is a great person, and me and all peers that have had him will feel an empty void at the beginning of next year when we look to his classroom and are not greeted by the cheerfully mischeivous old man whom we are all so familiar with. He told me aout some plans for this year, how he would leave the school "a little more shaken up than it was when he found it" and what he planned on doing. He wants to do a lot, one of his projects being to build a giant letter "F" (stands for failure) out of legos, in one of our staircases HUGE windows. But among some of his ideas were two that he thought I would take a liking to. I am not very inclined to deny him of these two ambitions, because i know they are relatively easy to build, I just have no idea how to build them. I have added them to my to do list as a semi high priority, as seeing we are already through our first grading period, and he does not have even a whole school year left.

1. Build a large (eg 5x7) 3-digit-display up / down counter with two buttons so that he can change the numbers either up or down by one number at a time. He wants this to be then mounted and framed in like a shoebox or something and decorated by his current students as "Mr. Stark's Countup/down to Retirement" or something like that. He wants to be able to edit it thought, because of snowdays or something, and he only wants to count school days. I was thinking a switch debounced counter circuit, but i'm seriously having a hard time getting anything to work.

2. This one is proving to be trickier. A remote controller battery powered volume controller that splices into the school's pa system above the drop ceiling tiles. Me and my otherclassmates always would be in the middle of a very important discussion with the teacher, and at least one time a week would be interrupted by and annoyingly loud screeching secretary telling us that the cheerleaders would be meeting in the south parking lot instead of the north one today.....blah...blah.....and on and on. We would try to talk over her, but her blahing was always loud enough to drown us out. It gets annoying. We want a small key-fob sized remote to be able to adjust the volume of the amplified signal of the pa system. And the lowest volume setting preferably be mute, just in case the announcement is particularly annoying haha. This one is stumping me.

Any help with these circuits would be greatly appreciated, I can do basic parts layouts, schematics, and board drawings for etching, so i should be able to easily fabricate any finished product.

Thank you so much, and any words of advice or encouragement you would have for a beginning electrician will be taken with the upmost respect.
Who's to say what is impossible?

Timothy Rasch
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school project help

Post by Timothy Rasch » Fri Oct 13, 2006 10:39 pm

Hi ,I am a consumer electronics technician[30 years of experience] that is out of work for 10 months.[the Boss retired] I suggest you look at Motorola mc14553 =NTE4553b datasheets [use Google search type in mc14553b datasheets]. They were taken over by ON Semiconductor. This is a 3 digit c-mos up counter 16 pin dip,multiplexed drive for common cathode displays and maybe you can figure out how to make it down count. I will research this for you . Anyway you can drive the clock input [pin 12]directly from a LM555 timer ic [pin3] operating on the same supply voltage . For the display you will have to use many leds in series for each segment just make sure all cathodes of each digit are connected together,this will take a long time to build out of leds . Also you can look up Nationals datasheet for MM74C947 4 DIGIT lcd up/down counter/latch/decoder driver .For driving leds with this ic you can use transistors like 2n2222 for buffering to the leds I think . I will research the proper driver ics for this, then you can build the driver circuits with transistors also. BTW see Nuts /Volts October Nixi clock.
Tim Rasch [email protected]

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philba
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Post by philba » Sat Oct 14, 2006 12:19 am

on the mute thing. you coudl use a relay to switch in/out a resistor in the speaker circuit. I'd guess that a 10 ohm, multiple wattage resistor would do the trick though you may need to play with the value. Control the relay coil with wired switch in the simplest case. Getting fancy, you could use an IR receiver to control the relay. Build in a 1 minute or so time out on it so it doesn't make you miss the important messages like "free ice cream" or what ever.

By the way, if you learn PICs you will discover that many things become pretty easy and cheap.

Timothy Rasch
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student needs help for project

Post by Timothy Rasch » Sat Oct 14, 2006 5:37 pm

Hi again I found out the National mm74c925n[4 digit] has the buffer transistors built in for the segments so it's easier to use,the counter is up counting only.The other bad new is the ic works up to 6v supply. For the time base you can divide the 60 hz /3600 = 1 count per hour [that's two divide by 60 counters cascaded or [6 decade counters =60 count so that will be 12 decade counters needed for a divide of 3600count] .For the count speed up to set the display where you want it you can use momentary switches from the higher speed points of the counter chain [like at the 6th decade counter out to the clock input;this will make the display advance 1 count per second, but you have to break the clock input normal connection before the other counter output is connected through the switch [a dpst momentary switch is needed here For the counter input]and then after the switch is released it returns to normal counting.You can use 6.3vac from a power transformer
and a resistor divider attenuator like 10k, 1k and a diode across it cathode to ground [the center of the resistors go to the 1st decade counter input for a cd4017b decade counter. I think the diode can be elliminated because the cd 4017b has a shaping circuit inside it. Use all cd4017b or other decade counters in the c-mos family for low power operation and a 7805 5volt regulator[tab is ground] and bolt on a heatsink or bolt it to an aluminum box with the circuit perfboard or circuit board. I think it's a big waste to build the display with discrete leds . My suggestion is to find the largest 3 or 4 digit multiplexed display you can buy ;try Digikey ,Mouser,ETC. Multiplexed means : each segment 7/digit is wired to the next same segment in the next digit all the way to the last digit going from right to left when looking at the display [the first digit on right side is digit 1]. You can use Radio Shacks individual digits [common cathode] and wire three or 4 digits together this way;this will work ok ,the digits are pretty large >.5" high. You should put the digits on a seperate circuit board and wire them to the main board. Hope I helped you out. Feel free to email Me. I could draw you a circuit idea and send it to you then. I myself started with electricity or electronics when I was eight[1961] or ten years[1963] old taking apart the toys of that era [airplanes] exploring crystal radios , using a Hallicrafters s38a am/sw radio. It sure is fun and exciting . I still don't know much about PIC programming ,a Friend of Mine does and learned on His own so it must be easy if the right information is found. I don't think your programmer that you made is enough, you have to have a programmer that comes with software and interfaces with a computer through a rs232 , usb cable . Try Jamico in CA. I think that's where my Friend got His and the PIC's . A pic can also do the divide by 3600 function or two divide by 60 functions or whatever ,so in other words it can replace the 12 decade counters and more. If you have a Friend that knows how to program pics please ask Him or Her if they can program one for you[tell them what you want programmed for the functions you want and have them explain how the output of the pic works] This is a enormous savings in space on the board and would really cut down on your building time for the project.
Tim Rasch [email protected]

Timothy Rasch
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student needs help on project

Post by Timothy Rasch » Sat Oct 14, 2006 6:14 pm

Hi again , I made a mistake with the switch, it is a single pole double throw momentary. Here are the connections [1pph from the 12th decade counter] goes to the top terminal ,the pole [center terminal goes to the 74c925 clock input],the bottom terminal goes to the 6th decade counter output [1pps]. The book that discusses CMOS is called CMOS COOKBOOK
by Don Lancaster Sams# 21398 c1977 first edition.I own the book. I think you can get it through your public library interlibrary loan department or through your school library. See if they can get you a updated edition. If you have a computer and scanner to scan the book you can save the entire book in the computer and then burn it to a cd instead of storing it on the computer harddrive. I have many books stored on my computer with a 40gb hardrive. I didn't burn them to a cd yet and have half harddrive full[20gb]. I procrastinate or put off things for a later time.
Tim Rasch [email protected]

macgeek10
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WOW

Post by macgeek10 » Sat Oct 14, 2006 8:46 pm

extremely fast response here, a++++ for this website.
I have been communicating via email with Timothy Rasch about the counter circuit, but any more help or suggestions with the volume controller and how to make it remote controlled would be great.

thanks
John
Who's to say what is impossible?

bodgy
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Post by bodgy » Sat Oct 14, 2006 9:50 pm

Somewhere I have a circuit using TTL/CMOS chips as a remote volume control.

On my list of things to look up.


Colin
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Gorgon
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Post by Gorgon » Sun Oct 15, 2006 2:41 pm

If you want a cheap remote, why not use a LED pointing device and a simple receiver that toggles a flipflop on-off-on ... for each blink. Controlling a relay that insert a resistance in the speaker line.

TOK ;)
Gorgon the Caretaker - Character in a childrens TV-show from 1968. ;)

Robert Reed
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Post by Robert Reed » Sun Oct 15, 2006 5:20 pm

I like your solution Gorgan, but maybe even simpler, would be to break out the line at a conveniant point and drop down to a simple L pad potentiometer mounted at the speakers pulpit. You know, the way they used to do it in the dark ages :grin:

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Post by Gorgon » Mon Oct 16, 2006 1:02 pm

Robert Reed wrote:I like your solution Gorgon, but maybe even simpler, would be to break out the line at a conveniant point and drop down to a simple L pad potentiometer mounted at the speakers pulpit. You know, the way they used to do it in the dark ages :grin:
Thanks Robert,
Yes, I remember the speakers from my school, ivory coloured boxes with wirewound rheostats(pots) to control the level. But they are hardly remote and not wireless. They could however, be combined with a big switch and a tennis ball to activate it with. :grin: Hit-off, hit-again-on and so on until you are out of balls. :evil:

TOK ;)
Gorgon the Caretaker - Character in a childrens TV-show from 1968. ;)

bodgy
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Remote volume control doomafligit

Post by bodgy » Mon Oct 16, 2006 5:20 pm

There are a number of ways to approach this - especially for the receiver end.

1. Take advantage of Maxim's sample program and get some digital volume control chips - or Linear Technology if your school has a tie up with them.

2. Get a BCD counter IC such as 4510 or similar, the binary count could step up or down the volume control chip, the mute function could be provided by a flip flop.

The remote controls could be an off the shelf design.

Alternatively even simpler would be something like an infra red pointer pen, where by the receiving circuitry would just recognise a beam had been pointed to it, which would switch a comparator or op-amp that would act as a variable resistor inside the speaker box - reducing or muting the volume.

Purchase a small 8 pin microcontroller from your favourite manufacturer, this could receive the Infra Red, decode and manage a electronic volume control chip. Get two of them and one can be a transmitter as well.

There is plenty of code available from Zilog to Microchip (on their websites as well as elsewhere) for talking to and from infra red devices. There is also seperate code lurking (not on their websites) for accessing things like VC IC's.

Colin


I before E except after C :D
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jollyrgr
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Post by jollyrgr » Tue Oct 17, 2006 6:49 am

How about a wall sized count down timer made of fluorescent tubes? Make a "seven segment display" using four foot light fixtures for the vertical segments and two foot tubes for the horizontal. A seven segment display driver such as the 7449 can be used to decode the segment. Counting can be done with with something like a 74193 counter.

I don't do PICs but using a PIC and a decoder should be super simple.

Just a thought.
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