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The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

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Old 04-09-2013, 09:04 AM
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edwardholmes91 edwardholmes91 is offline
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Default Toy Organ

Hello,

During the summer holidays I will be working at a summer camp in PA, USA teaching simple electronics to children between the ages of 7 and 15. I have been asked to come prepared with a selection of different circuit that I could teach the children and that they could build.

In search of circuits I came across Forrest M. Mims series of Engineer's Mini Notebooks and decided to buy them. I have to say they are an interesting read so far and there seems to be lots of fairly simple circuits that would be suitable to teach to children.

The "Toy Organ" on page 23 of Volume I struck me as a fun circuit to teach the children, without requiring too much theory. For those of you without access to this book I have copied the circuit onto the computer:



So my questions are... it surely must be possible to instead of using capacitors that seem to be in the E6 range use resistors? If my understanding is correct (I'm scratching my head here, because we're going back a number of years since I studied this sort of stuff) the 555 timer uses an RC setup to provide it's time base? Therefore, a range of resistors could be used and a fixed capacitor value instead?

Also thinking about fabrication, using tactile switches would be an expensive solution. Therefore it got me thinking about touch sensitive switches. Correct me if I'm wrong... but a Darlington pair could be used to create a touch switch, which would operate when you touch your fingers on two PCB pads?

The circuit suggests 15 capacitor values, but you could just as easily use more or less. From memory I believe a Darlington driver IC package is available in both 7 and 8 pair versions? Using two would give you 14 buttons and in effect two octaves?

This website looked quite useful because it gives the different frequencies of notes on instruments. As can be seen, the toy organ more than covers a lot of the range. The human ear can only hear 20Hz to 20kHz I believe, so the range isn't a problem.

I believe that touching more than one switch at once would give interesting results... but this isn't a problem, I'm not looking for a polyphonic solution or anything fancy. Just a fun circuit to teach kids, whilst explaining the theory behind it.

Looking forward to hearing from people, if there is anything else that I can provide let me know and I will do my best
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Edward

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Old 04-09-2013, 01:34 PM
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The toy organ is a great idea. However, using capacitors in order to arrive at the correct tones would be a royal pain. There is a larger selection of precision resistor available than there are capacitors.

I would opt for a single capacitor and use the push buttons to select the resistors.
For extra trouble and expense, you can use trimpots instead of fixed resistors. This would allow you to adjust each note independently.
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Old 04-09-2013, 01:41 PM
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The administrator over at Electro-Tech-Online published a circuit for a toy organ, doing exactly what you describe. I would NEVER choose to change the capacitor values. As MrChips mentioned, there is a much larger selection of resistors out there. Here's the link: http://www.electro-tech-online.com/c...toy-organ.html

Hope this helps.

Regards,
Matt
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Old 04-09-2013, 01:43 PM
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Quote:
Originally Posted by MrChips View Post
For extra trouble and expense, you can use trimpots instead of fixed resistors. This would allow you to adjust each note independently.
I did that once, but if you connect them in the way shown in the ETO link, you have to adjust the first one first, since all the others depend on it. However, if you can figure out how to have each pot set up individually, it would make it much easier.
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Old 04-09-2013, 01:55 PM
RayInMS RayInMS is offline
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Edward -

You asked about this in my other thread. Here is the one I built.

http://www.talkingelectronics.com/pr...ircuits.html#1
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Old 04-09-2013, 02:41 PM
elec_mech elec_mech is offline
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I can't speak toward touch buttons, but Tracecom suggested a cracklebox in another post I read today and that uses touch pads and generates tones. Video here, plans and schematics here. Looks interesting.

Quote:
From memory I believe a Darlington driver IC package is available in both 7 and 8 pair versions?
ULN2004 (7 outputs) and ULN2804 (8 outputs) - both will work with 9VDC.

Another thought is using paper clips and nails or screws as contacts to act as switches.

Not sure how many projects you'll be working on, but I was part of college club that taught basic electricity principles to education majors. By far the most well-received project we did was making simple motors. The most common one I found is often referred to as Beakman's motor (taught on a science show I think).

We bought 12 packs of AA's from the Dollar Tree, 1/2in magnets from craftstores or Walmart, and I got the magnet wire from work from scrap. Instead of paper clips, I found attaching #2 safety pins to the AA battery with a rubber band saved a lot of time and hassle. The pins were found at Hancock Fabrics - I mention this because I went to several stores and most only sell packs of mixed-sized pins. I think any true fabric store will carry these. This is a cheap, easy to make project. Even those who had difficulty kept working at it when they went to other stations.

Another simple motor is the homo polar motor. While it appears simplier, it's a little harder to balance and get going. We did not have much interest in this one at all.

I don't know how complex you're going to go, but a 555 monostable timer might be another fun one to make. The kids could make their own timers for races, baking, etc.
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Old 04-09-2013, 03:01 PM
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Quote:
Originally Posted by RayInMS View Post
Edward -

You asked about this in my other thread. Here is the one I built.

http://www.talkingelectronics.com/pr...ircuits.html#1
Avoid talkingelectronics whenever possible. The guy who runs it doesn't know a thing about electronics, and often makes stupid mistakes in his circuits. If you use a circuit from talkingelectronics, I HIGHLY RECOMMEND checking it against other circuits first. I, personally, just don't trust the site at all.
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Old 04-09-2013, 05:15 PM
RayInMS RayInMS is offline
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Quote:
Originally Posted by DerStrom8 View Post
Avoid talkingelectronics whenever possible. The guy who runs it doesn't know a thing about electronics, and often makes stupid mistakes in his circuits. If you use a circuit from talkingelectronics, I HIGHLY RECOMMEND checking it against other circuits first. I, personally, just don't trust the site at all.
Good info - thanks.
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Old 04-09-2013, 07:49 PM
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I have recently got a collection of old elektor magazines dating back to 1975. And I think I have come by some circuits for toy organ. However I think the classic light dimmer circuit. Connect to the mains would ideal for that age segment of age (Err... just joking)
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Old 04-09-2013, 08:45 PM
absf absf is offline
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Quote:
Originally Posted by DerStrom8 View Post
Avoid talkingelectronics whenever possible. The guy who runs it doesn't know a thing about electronics, and often makes stupid mistakes in his circuits. If you use a circuit from talkingelectronics, I HIGHLY RECOMMEND checking it against other circuits first. I, personally, just don't trust the site at all.
Nevertheless, you can use the site to get project ideas on 555 projects. It is amazing what the 555 can do.

A 555 metal detector or a 3-player "who press the button first" game show timer using 555 might be good projects too.

Allen
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