you can disable the demultiplexing by removing a jumper (I must suggest the use of a removable jumper here, like those used to define master/slave in HDDs).
Not sure why you're disabling the demux now that you're using Outputs O
0 thru O
3 (see section about pins 4, 5, and 6 below), but having the option of jumper pins for grounding input A
2 (disable switch) sounds good.
Pads are now equally spaced. This way one can decide to use 5.08 mm screw terminals (sorry but I don't like those tiny 2.54 mm spaced) or solder directly the cables on pads.
You may not like them, but some users might.
Consider adding 2.54mm pitch through holes for Dupont pins or small screw terminals in parallel with the current 5.08mm holes for large screw terminals so users can choose whichever they prefer.
Notice that any "138" demultiplexer will work (74LS138, 74HC138, 74HCT138).
The LS and HCT series chips will be fine, but will the HC (High-speed CMOS) logic levels work with typical IPac/Arduino setups?
http://forum.arcadecontrols.com/index.php/topic,163889.msg1728853.html#msg1728853Notice that to work correctly, inputs on your receiving device (i.e. Arduino...) must be set to "input pullup" (input forced to HIGH, activated by LOW input signals). If your encoder force you to use input puldowns (shame on closed hardware) you can use a 74LS238 in place of the 74LS138.
Sounds like you can convert the board for an "active high" encoder by using a 74__238.
- That
should make this board work with "Zero Delay" encoders, right?
I used the IC disable pin (G1) to disable it ( ), forcing pin A2 to ground and thus limiting the truth table to the "green region".
That first half doesn't sound right.
Looking at the logic symbol on your truth table, there is a boolean AND gate with 3 inputs (pins 4, 5, and 6), two of them inverted.
- Ground on pins 4 and 5 (E
1 and E
2) and 5v on pin 6 (E
3) satisfies all three conditions for the AND gate which allows access to lines 4-11 of the truth table which includes the "green region".
- If you have a logic high on pin 4
or a logic high on pin 5
or a logic low on pin 6, you will be confined to lines 1-3 of the truth table.
There are some typos in your Daytona Truth Table:
- Gear 2 should be Output
O0 (pin 15)
- Gear 4 should be Output
O2 (pin
13)
Looking at the board, you can see that:
- G1 is connected to pin 14. (good)
- G2 trace is on the back of the board, it should already be connected to pin 15.
- G3 is connected to pin 12. (good)
- G4 is connected to pin 11. (should be pin 13)
By using A2 as disable input (as Scott suggested) could let us introduce an optional neutral output, but I don't think it is really necessary.
I agree that a separate output for neutral is not necessary.
Scott