are these circuits ok?

[joejoe]

hi, heres the pics of the circuits im having trouble with



this is used for putting momentary contact between wires that come from a cannibalized keyboard.

circuit 1 is supposed to turn an spdt switch into a momentary ouput via the 4n25 ic, it was intended to drive a servo motor, but should it be able to work in this case as well? (i got the scematic from a site that is using it for the same function i want to use it for) then when the switch is in the opposite indication it is shown, power goes through the ic, closes the transistor, and when the capacitor gets filled it stops the current from cunducting basically it acts like an open in the circuit for as long as the switch is in that position, (it doesnt pulse with the rate the cap fills and discharges, it just fills and stops) when the switch is put in the indication i have illustrated, the current will flow from the cap, through the switch and through the ic triggering the transistor until the voltage is back in the cap or disippated, then when the switch is thrown again it repeats the cycle.

circuit 2 basically i want it to trigger the 4n25 ic until the cap fills. when the switch is in the on position, and then thrown to the off position, then thrown back to the on position, it sends voltage through the ic momentarily until the cap fills. i dont know if the voltage already in the cap will prevent the ic from being triggered or what, thats what i am asking you fine people.

circuit 3 well, is just a hybrid of circuit 2, performing the same function but instead of there being an off position on the switch, it will trigger voltage through another ic, and back and forth as the switch is thrown.

so i just want to know if the drawings are functional. if you have a better idea using some other CHEAP components please tell me. thanks! (btw cost per switch including all the wiring and ic's is about $3, so if it works feel free to implement it in your work)

[joejoe]

hmmm picture doesnt seem to want to show up. the sizes is much smaller that 800 pixels . and its only 14k. if you think you can help, tell me what to do. or if you know somewhere else i can post the picture.

[SilverFox441]

Why not post a link to the site you got the pic from?

[chuckcrc]

Using a bashed keyboard can be very tricky, because of the sanned matrix you can get ghosting etc. I have used ICs to interface into the keyboard (4016 or 4066) and found that the quad switch 4016 had too high a on resistance for the keyboard to recognise , so I had to double up the gates. I need to know what the 4n25 ic actually is before I would be able to help very much.
I found the IC type reed relay (approx AUD$3.25) worked very well with an elecrolytic capacitor and an spdt switch. One thing I will say is that using a capacitor discharge type ssystem can put all types of spurious noise and spikes back thru your power system which will affect ICs. Usually you should have a decoupling cap between the Vcc and GND points of your IC.s to help minimise this.
cheers
chuckcrc

[joejoe]

i seem to have bad luck with the forums, if i click on the link from the email it send me when someone responds to my post it logs me out of the forums, when i log back in and click on reply to reply to my post it tells me to log in. so i log in, click reply and it tells me to log in. until now i just tried going through the main site and now it works fine, pic still doesnt work though, it only resembles where i got the idea from and i drew the schematic in question myself. i have posted my problem on other forums and have gotten some good advice, including the use of 4066 ic's. so ive redesigned the schematic to use 555 timers in monostable (one shot) mode to trigger the 4066. heres the new schematic:



darn pics just dont wanna post..........if its ok with the mods ill tell you how to get to my post on the other forum, go to www.gideontech.com click on forums, go to the "electronics" section and look for the post titled "are these circuits ok?" thanks fellas

btw, if this schematic works and you want to use it, dont use electrolytic caps. dont ask me why, its recommended that you avoid it. as for the cost of the new circuit including the switch and wiring its still around $3.00

[SilverFox441]

From what I can gather the main (electronic) reason for these circuits is contact debouncing (preventing a train of signals from one switch contact). You seem to be getting good advice over there so I'd go with what they are telling you.

Two points though.

• You are probably going to want more than one of these circuits in your project so investigate using 556 timers (dual 555's) to save components. A 556 is nothing more than two 555's in one case, but watch the pinouts.
• Electrolytic capacitors have a lower leakage threshold than other types and pose several added dangers. Follow the advice and use the recommended types instead.

[chuckcrc]

Joe Joe
I have gone to that site where your cct is and had a look.

Your cct won't work in a toggle function because when you charge and then discharge a capacitor the polariteies of the charge ( read battery) reverse. The optocoupler has an LED type device in it . These are polarity dependent. So it will only work on one cycle.The keyboard IC has in built de-bounce ccct in it so I don't think this is an issue.

The one shot 555 timer is an option however there is a lot of cct board soldering and wiring to make these work. Also the use of 4066 Quad switches are ok you have to watch the turn on resistance. I have designed and built these ccts , variations of these ccts are currently working in my simpit.

Let me speak with the voice of someone who has built a pit with a bashed keyboard. Of all the options to choose in building a simpit , let me tell you this is the worst option you could pick. The amount of design , cct board construction and wiring up , and avoiding noise spikes etc is huge. These bashed keyboards are not cost effective. If you must use a bashed keyboard then I suggest you buy should IC packaged (14 pin package) Reed relays. These will operate on any polarity. They are cheap and all you need is the spdt switch which you have to buy anyhow and one elecrolytic capacitor. They are easy to wire up. They are almost immume to noise spikes, they are fast operating and you don't have to worry about any ESD percautions.

Now with the benefit of hindsight , I  have bought a Plasma USB controller card from BetaInnovations that can have up to 64 buttons inputs , 16 axis ips etc and heaps of other devices. This unit was not available when I started design work on my simpit 3 years ago.These make the construction of your simpit so much easier and the cost is about the same or less. My unit, cost me with freight from Canada to the other side of the world  Australia ,about $100 Australian. (this is about equal to 3 slabs of beer ! but sometimes the sacrifice is worth it!!)

Anyhow what ever you decide to do I wish you the best of luck.

cheers
chuck  

[joejoe]

the plasma v2 looks pretty good, very good actually. hmm. thanks for pointing me to it. and about the wiring of all these ic's yeah your right, unless i etched out a circuit on a board then im gonna have to dedicate alot of room for all this, not to mention the fact that it may not even work properly once i finish putting it all together. theres also a sale on their website until july 9th, yeah ill buy it instead, just putting the prototype circuit for my design was getting tedious. thank you very much for your help chuck and silverfox.

it has certainly been a learning experience for me, before i tried this project i had no idea what ic's did, or that there were so many different kinds. it is going to be a tad less fulfilling to me though, just buying a usb controller instead of building my own, but i think ill deal with it!