Books of the Bible

[Zecreamdix]

Hello,
I am a Sunday School Teacher in my spare time. At a young age we begin working with our kids in attempt to teach the Books of the Bible and in order. I have a friend that has a CNC Router in which I was thinking of having him take a 4" x 3" sheet of oak and have him mill in the Books and give me a hole for an input push button to be installed. A corresponding second for a green light for a correct choice. This will make me need 70 Inputs and 70 Outputs. Is there a way to make this work without spending $1000.00 on expansion slots or using an HMI?

 

[5618]

Some random thoughts on this:

-This might be a good application for a Raspberry Pi or Arduino, in a few possible ways. I haven’t seen that much GPIO on one setup, but I expect it’s available. As an input device, one could be setup to output a string to a PC or PLC that corresponds to the input actuated.

-Two pole switches are common. To reduce inputs, you could multiplex switches to each turn on a unique pair on inputs. Sixteen inputs would provide 64 double inputs plus 16 singles to do 80 switches.

-Multiplexing outputs isn't as friendly. It would take a bunch of relays to multiplex an array of outputs provided you only will ever need one light at a time.

-The common PLC way to do this would be all touch screen. That’s fine for industry, but a wooden board sounds really cool and special. I hope you do it.

-Once upon a time I might consider doing something like this with 7400 series logic. Nowadays, a FPGA would be the way to go. Maybe not so practical for a one-off system, but it’s another random thought

-So, with a Click… one 16 point in, five 16 point out, is about $380-ish, plus the controller. And a bunch of switches and lights… And a power supply… And wire it…

 

[Steve Bailey]

How are you going to drill 70 holes and have 70 readable text strings in a 4" x 3" sheet of oak? I presume you mean 4' x 3'!

You could reduce the number of inputs needed by assigning switches to rows and columns and using the combination of two switches to define a single book. A matrix of 8 rows and 9 columns requires only 17 inputs and gives you 72 unique combinations of one row and one column.

 

[Zecreamdix]

Yes, you are correct. 4' x 3' my mistake.

 

[robertmee]

How are you going to drill 70 holes and have 70 readable text strings in a 4" x 3" sheet of oak? I presume you mean 4' x 3'!

You could reduce the number of inputs needed by assigning switches to rows and columns and using the combination of two switches to define a single book. A matrix of 8 rows and 9 columns requires only 17 inputs and gives you 72 unique combinations of one row and one column.

To elaborate on what Steve is suggesting, you can also do the output lamps with a matrix and a bunch of blocking diodes. Pinball machines used this method for most of the 80s to 2000s. Search pinball lamp matrix. They also had a switch matrix similar to what Steve described for inputs.

 

[Zecreamdix]

Thank you for responding.

 

[drbitboy]

It could also be done with one analog input (minimum 7-bit resolution) and a voltage divider with 69 resistors.