Here is an extract from the paper I mentioned.

Originally Posted by philba

I'm not sure what you are disagreeing with. This isn't rocket control, it's just a couple of signals. If you dispute "not worrying about it" then you surely took my comments out of context - ah vs al is not some mysterious thing. that's all I was saying to him. What I was trying to say is that the AH/AL concept is very useful.

But I slightly disagree with your suggestion of an ssi solution (and/nand/on/nor) - 4-16 demux is simpler to wire up and far easier to understand. I agree. If you go back a few posts, you will see that I said that your's is a good solution.
even if he has to put inverters on the mux outputs. chasing though the terms of your solution is much harder for a newbie to understand. Either one will work but I'm trying to be thoughtful of the OP's experience level. My point is that if he understands my solution, he will then be in a better postion to understand the logic diagram and truth table in the 74HC154 data sheet.

By the way, the best way to simplify is to use karnaugh maps to pluck out the relevant terms. but that's well beyond this problem.

I used Karnaugh maps to derive the circuit I posted.

hi ryan,
Which version of the circuit are you referring to?

Any diagrams to post, will help.

Here it is:

basically, when joystick is unplugged... I get no continuity between the terminals of wire Z and each of the blue wires . this is correct

when plugged in, there is continuity on all of them (wire Z, and each blue wire)
this is wrong, as its trying to push all 6 joystick buttons at the same time.

the red wire is the power supply from the USB, and the black is the USB power GND. When I put a my meter across wires X and Y, I get about 4.5v. When I put my meter across Z and Y, I get 2.5V when none of the S1/S2 etc are active.

EDIT: there is never any continuity between Z and X

I think I've wired something incorrectly...
Help! Please!

Thanks

hi,
I havnt been following this post for a couple of days.

The 74154 is a TTL device, with active low outputs. I thought philba recommended a CMOS version of the device???

The outputs will be high, around 3 to 4 volts when none of the S1 thru S5 push buttons are pressed.
To set '5' low,[1st] both S1 and S3 must be pressed.

I'm sorry this help is limited, I'll look thru the back posts and try to get up to speed.

EDIT: I assume that you have got the +5V and 0V lines connected to the 74154?
I have got to ask, just in case!

Hi Eric

I am using the 74HC154. Which is CMOS right? Sorry, I just used philba's attached diagram which had 74154 as the label from the beginning.

The V+ and V- are connected, forgot to add that to my diagram, V+ is common with red wire on my new diagram and V- is common with wire 'z' on my new diagram.

please check the above diagram again, I have updated it with the Vcc and GND connected, and the full name of the chip.
tnx

hi ryan,
Understood.

Looking back at your earlier posting.
>> I tapped into the V+ of the joystick (my meter reads 2.5v from the power of the joystick to the common
of all the gear1-6 switches on the joystick board).
The Common of the S1 to S6 should be at 0V [Gnd], not 2.5V

>>
There is another black wire on the board which has NO continuity to the gear 1-6 common, but when I read the Voltage across that main black wire and the joystick V+ its about 4.5volts.

This Black wire is the 0V [Gnd] and should be connected to the 0V of your pcb, pin 14 of the 74HC154 and the S1 to S6 Common.

Recapping:
The RED wire +V should goto the top of the resistors, as you have shown and pin 24 of the 74HC154.

The BLACK wire 0V should goto the Common of S1 thru S6 and pin14 of the 74HC154.

Dont use your meter on Continuity to test the circuit when the ic's are connected.

Remember when you have connected as described, the output pins of the 74HC154 without any gear switches pressed will be high, about +4V.
The selected output will goto 0V when the correct gear switch is pressed.

hi,
That looks OK to me.
When its connected up and plugged in check the voltages with your meter.
Lets know what they are.

The problem with testing for continuity with ic's connected is that some meters when on the 'ohms' resistance range can have a voltage on the leads due to the meters internal battery. Depending on the type of meter it may apply a 'reverse' voltage on the ic's. Also you will get misleading readings caused by pathways thru the ic's.

Ok, plugged in and put on the joystick test utility again, now it seems a bit better, when powered up, none of the joystick buttons are on... But selecting any combination of S1,S2,S3,S5, will also not yield any change.

Point of interest: If I just touch wire 'z' to wire 'x' (this was a last resort test), all six of the buttons y1-y6 become active.

One thing I dont understand about this circuit is that wire 'x' and wire 'z' are not common, so how can it complete the circuit ever, unless I wire them together (which makes all six permanently on)

Getting 5V between y1-y6 and X when all of switches S1,S2,S3,S5 are open
Getting 1v between y1-y6 and Z when all of switches S1,S2,S3,S5 are open

I get the same 5v when I try activate y1, this is on wire X
I get .5v when I try activate y1 (so it drops .5v), this is on wire Z

I haven't disconnected and tested the outputs of the '154 yet, will do that a little later.

I'm pretty sure the chip is in the correct way, I soldered on a chip holder too. The actual chip has a full circle on the bottom, and a semi-cicle indent on the top, the datasheet shows just the semi-circle on the top, so thats how I did it...

Not too sure what inputs the joystick requires. I thought you guys said it was CMOS, so it had to be active low. Nonetheless, if i diconnect my newly built cicuit enirely from the joystick and take a jumper and bridge wire Z to terminal y1, it activates that button, without any external voltage whatsover.

Thats what I didn't really understand about this whole circuit. I thought we could just close each switch remotely, instead of introducing voltage from an alternate circuit.

I'm very confused now!

EDIT:
Tested the inputs, they work perfectly, chip is wired fine aswell.
The outputs: Seem to be great aswell, I get a mutually exclusive Low output for each corresponding gear. ie (y1 is high 5v+ in all possible gear combinations including neutral, except for 1st gear.) This is using wire y as the anode on the multimeter.

This seems like a good thing, the circuit seems to work perfectly, except its not activating the gears on the joystick.

Im am so sure that it has something to do with the fact that wire 'Z' on my latest diagram does not have continuity at all with 0V gnd, whereas that is the common opposite terminal for all the joystick buttons y1-y6.