About John Penton Expertise I am happy to answer questions on semiconductor devices - in particular high-voltage devices.
Also any electronics or physics homework questions.
I`m not a semiconductors professional (at the moment), so no really in-depth questions please.
Experience Degree level education in Natural Sciences and Electrical and Information Sciences.
My final-year project was in high-voltage power MOSFETs.
Currently work for ARM Ltd, designing microprocessors.
Expert: John Penton Date: 6/14/2002 Subject: signal switching circuit
Question Hi, my background is in mechanical engineering so I have a good grasp on physics and most things technical, but I am not very familiar with cicuit design, etc.
I have an input device with both analog and digital low voltage (TTL I think) inputs. I would like to make a "black box" (placed in line between my input device and the device being controlled) in which the input scheme could be reconfigured in any number of combinations without having to rewire the input device. For example: The input device has 3 momentary digital switches, buttons X, Y and Z. I would like to swap the X and Z button functions. That seems like it would be fairly simple, but I would also like to be able to reconfigure all buttons to have the same function; that is, I would like buttons X, Y & Z to appear as X to the controller. There are also 2 analog inputs that I would like to be able to swap or make either perform the same function.
I can sketch out all the possible reassignments, and it seems that it is just a matter of intercepting the signals and redirecting them as necessary to get the desired effect.
How might I go about achieving this type of in line reconfiguration? Is it possible? Are there any components available that can do this type of circuit rerouting/combining etc.?
Thank you in advance for your help.
Best regards,
Jay
Answer Sounds like a simple logic problem to me. Get some gates and arrange them to produce the desired effect when driven by some control signals. In your first example Xout = (Zin AND SwapXZ) OR (Xin AND NOT SwapXZ) (and similarly for Zout). In the second Xout = Xin OR Yin OR Zin. I suppose you can combine these Xout = (AlltoX AND (Xin OR Yin OR Zin) OR (NOT AlltoX AND ((Zin AND SwapXZ) OR (Xin AND NOT SwapXZ))). Get the picture?
With regards the analogue signals - you can buy chips which have on them analogue switches (like mechanical switches only they are controlled by a digital signal). Use one of these to connect each input to each output, then control them using logic in a similar manner to above. I suggest that your logic makes sure that you never connect the two inputs to the same output. If you want to do this, then you will have to think harder about how it will work. If both input A and input B are controlling the output and say A=6 and B=3, or the output 3 or 6 or 4.5? All are possible, but will required more complex electronics (involving op-amps probably).
HTH John
