Another question on the LED resistors.  

Looking at the LED for the 9V circuit, it is a 2.1V drop at 20mA.  Given the 9V supply, we should expect to see a 360Ω resistor, but the BOM specifies 1K.  That leaves the LED a bit on the dark side, but serviceable.

For the 3V circuit, the LED has a 2.05V drop at 20mA.  Given the 3V supply, the resistor should be 51Ω, but the BOM has it as 4.7K which makes for a really dim power indicator.  

For the big red LED, what voltage are you expecting to go to it nominally?  With the 100Ω resistor, there isn't much of a drop. 

Am I missing something obvious?
 

20 mA will probably light up the whole room. Modern LEDs are very efficient, and a few mA suffices these days. 20 mA in datasheets is a holdover from long ago when that was the max rating.

Yup!  I usually shoot for 5-10mA max with basic diffused LEDs, but you have to watch out for the bright ones for sure!  

So, for the LEDs I used non-diffused high-MCD rated LEDs with lower current for extended battery life.  Both are fine as far as I'm concerned - easy to see when on, but even if the switch is left on for a while it won't eat up the battery life.  I've actually used much higher brightness LEDS that work fine with less than 1mA!  That being said feel free to change it on your board if you want.  The 100 ohm resistor for the 10mm LED is basically chosen to prevent it from burning out if it's accidentally wired directly to the voltage source.  The value works fine for the experiments.  You can choose a different resistor also if you want.

A couple more notes from assembling the Sensors/Outputs board

1) For LED3 (XLM2MR01D) there isn't a flat side, instead it is the short leg of the LED.  Someone might spend a long time (myself included) looking for the non-existent flat side on that big LED
2) The 9V battery Resistor and 3V Battery resistors really need to go on the back of the board so that you can snug the battery holders solid to the board.
3) The footprint for the Thermistor (TH1) is a bit tight.  I'm thinking that you are expecting it to be raised up from the board a little, but I'm not quite sure in this case.
4) It might be worth adding to the BOM the screws for mounting the battery clips to the board as well as the standoffs for mounting the board on the base board.

1)  Yes, 10mm LEDs often don't have a flat, or sometimes I've seen them with two flats!!  ALWAYS check these with a meter before installing if you are uncertain - if you have a diode setting that makes it pretty easy.

 2)  For the most part  I was trying to hide any components that were not directly part of the experiments, hence the resistors on the bottom of the board.

3)  Yes, the thermistor was maybe 0.2" off the board.

4)  Sounds good!  I'll see if I can revise the BOM this week; appreciate the second set of eyes!

Also, instead of putting the LED Resistor on the back of the board, why not hide it under the 9V battery with the other Resistor.

I found another oddity with the BOM for the 4 resistors on the Sensors/Outputs board

The BOM has
R1 - Meter Resistor 10K
R2 - LED Resistor - 100ohms
R3 - 9V Resistor - 1K
R4 - 3V Resistor - 4.7K

However the silkscreen on the board identifies them in the opposite order

R4 - Meter Resistor - 10K
R3 - LED Resistor - No value
R2 - 9V Resistor - No Value
R1 - 3V Resistor - No Value

I believe that the board labels are correct.

However, it might warrant an update to the board.  I've got a couple of suggestions if you do manage to update it.

1) The foot print for these resistors is narrower than the other board which used a .4 spacing (which is is the smallest slot on the resistor lead forming tool.  Please bump it up to .4

2) Don't restart numbering with this board, Make them R11, R12, R13 and R14 to avoid any confusion.

3) Make the footprint for the transformer have a spot for the extra output pin (going nowhere) and the solder down for the case.

Has anyone seen an online PDF of the original 65-in-one-kit?  I  found a version of the 160:1 kit at https://www.zpag.net/Electroniques/Kit/160_manual.pdf

I found the 75 in one at https://www.radioshackcatalogs.com/flipbook/m-science_fair_kits_75-in-1_electronic_project_kit_28-247.html along with a bunch of others at  https://www.radioshackcatalogs.com/science_fair_kits.htm but the 65-in-one seems to be awol

Great project Tom!  Thank you for all your effort on this! 

I've ordered parts and am about to build, but I've discovered a couple of questions about the parts from the posted BOM

1) SPK1 list a quantity 2, TX1 a quantity 3, and S1 a quantity 4 but I think that is just an excel auto increment and they all should be quantity 1.

2) SK1 is listed as being an SP570408-1 which has a 57mm diameter, but the 3D printed case is for a 50mm diameter speaker.  Should the part actually be SP500408-1 which looks like it would fit.  With the SP570408-1 speaker, it is larger than the screen printing on the board.  My choices at this point seem to be to order the smaller speaker or to tweak the model for the Grill to hold the larger speaker.  Is there an original model available to work from?

3) TX1 specifies a 42TM013-RC which seems to be the right physical size and is listed as a 11.486:1, but the silk screen on the board says 125:1 and the part has three taps on the secondary while the board is expecting only two taps.  Also, the board doesn't have any holes for the side tabs, so I am assuming you just cut them off.  Is this correct or did I somehow find the wrong part?  The specs of the 42TM013-RC part at Mouser seem to be appropriate for driving the speaker, but I want to make sure it matches what you expect.

4) (this is very nit-noid) The BOM lists C2 as a .02uF capacitor, but B32529C1223K000 is actually a .022uF cap.  Given that the range of a 10% tolerance includes both and 0.022uF is the standard, I am assuming that the BOM just dropped a digit.

Hahaha, good catch about the auto-increment. Obviously 2 speakers are needed for the extension to stereo, and you can never be too careful, so 4 power switches. 🤪

Lol!!

Thanks John!  Glad you’re doing the build!  Thank you for the questions and catching the errors; I will correct them.  To answer your questions:

1)  Yup!  All quantity 1.

2)  I think the speaker should be a SP500508-1.  Unfortunately, I went through about six different speakers and lost track.  I will see if I can verify for sure…I know the print file / size is correct.

3) Whoops!  Yes, I didn’t have the turns ratio, it was the impedance ratio, my bad.   I’m only using the two outer taps on the secondary (cut the CT wire), and I cut off side tabs.

4)  I stuck with the original values from the original 65-in-1 even though they are not exactly the same as the parts.  Same as the 0.05 which is really 0.047uF

I'll get back to you soon hopefully on the actual speaker.

Thanks again!

Perfect!  I look forward to the updates but will be moving on to building in the next week.

Hi all!  If you happen to be at Supercon today I will be doing a lightening talk around 10am on the project.  Hope to see you there!!

So beautifully done Tom.

Thank you!  I hope others will be able to use the kit!!

I received something similar made by phillips in the early 70s as a christmas gift. I played countless hours with it. It determined my future hobby and my interest for electronics that became my livelihood !

Btw, voltage isn't considered as a physical value, it's a current thru an impedance.

Can You create a different language info/tag ? For example Polish.

I thing power in center is better idea than on right.

Not sure if the original kit had plans for making a Volt meter but for teaching circuits and Ohm's Law, voltage and current meters are important tools to have. So besides making circuits, having enough components to make the play circuits AND have a volt meter wired up for the learner can explore the circuit would be great.

I was also thinking it would be handy having the xformer ratio listed under the part and maybe a "Power Sources" label added to the 9v and 3V outputs. Would also like to see the relay diagram but would be tough to fit that in the space. Hopefully it's on the side of the part.

Doug - great suggestions!  The original did have a current meter - I'm planning on having a couple of experiments with series / parallel circuits, etc where they can use the meter.  I'll definitely add the Power Sources label and turns ratio on Txformer.  I'll probably have enough room for the relay diagram too like the original.  Silkscreen layout seems to always takes more time than the original component layouts!! :-)

I would love to buy this kit and use it as a build night activity for our ham radio club. 

Once I get everything finalized I'll post the build files.  However I'm also open to selling kits at some point - will let you know!

This kit is fantastic and as with others, brings me down memory lane as I had the 100:1 kit.

Currently trying to teach Middle School kids basic circuits and Ohm's Law using alligator clip leads and resistors and now starting a soldering lesson. Would be great to go in reverse on a kit like you have here. ie teach soldering first, make the kits and then use them to learn circuits! I like it better than the $50 Arduino Super Starter Kits I've used for small groups. Nice work.

Thanks!  Yes, that was my thought too - the soldering would be pretty basic - large scale pitch / through hole components would be an easy soldering project.  I also agree with the starter kits - the price point is good, but working with traditional breadboards is tough for younger kids.  

I love the breadboard kits but when teaching circuits and following electrical paths things get lost. Not to mention dealing with inserting components correctly and getting the jumper wires into the correct row. Gotta have a good grasp of a circuit and the way you did it, as did the springs, is ideal for the beginner. CS is starting to become a HS requirement and I would love to see basic electrical circuits be part of that.  I'll keep an eye out for your build files and thanks for sharing.

Wonderful!  Seeing this is like bumping into a long-lost friend on the street.  Now all I need to be truly happy is a few Tab books; I read and re-read my copy of "Build Your Own Working Robot" till the book fell apart.

Glad it resonates with you! I feel like I grew up in a magical time as an electronics hobbyist. So glad there are websites out there that still have copies of magazines, catalogs, etc. I read BYOWR so many times - I think I still have my original copy!

I had that book too!

Looked this up in the 1976 Radio Shack catalog -- $21.95. That must have been a fortune to my parents back then -- equivalent to $119 today! Wow!

Page 92 if you're interested: https://www.radioshackcatalogs.com/flipbook/1976_radioshack_catalog.html

Wow, that catalog was a trip down memory lane!  So many memories of things I could never afford when I was a kid.  The price on my 65in1 was $17.95 - makes me appreciate my Dad's willingness to help me get into electronics!

And one of the main goals of this project is to make something similar with a low cost point so they can be used in homes / classrooms, etc. without spending a lot of money...

Pretty sure this 65-in-1 is the exact one my parents got me for Christmas when I was about 11 or maybe 12. I hadn't really thought much about electronics before that, but I was on fire for the field after building that first circuit. That one present kicked off this whole crazy journey. Thanks Mom and Dad!

Thanks for the memories. Looking forward to seeing where this project goes!

I think this was about the same age I got mine too!  I found this one on eBay to show other friends / students how I started my path on learning about Electronics.  I miss these days of P-box kits and buying parts at Radio Shack.  My Dad also payed for my subscriptions to Popular Electronics and Elementary Electronics, which also had a huge impact on my journey too.  Looking forward to developing and sharing the project!  Cheers!