Electronics [success!] computer driven remote-controlled car

hello everyone. i'm here with a bit of a question. i dug my skydriver out the other day and realized that the controller is probably very simple inside and then i decided i'd really like to be able to drive it via the computer. here are some images to get started [please excuse a bit of blurriness, my only digital is my cell phone and they're still clear enough to understand]:


an image of the car itself. it's two front wheels are powered independantly, allowing you to drive one forward and the other reverse simultaneously.


a broad shot of the exposed controller. components are on the bottom, but there's really not much to this.


here you can see the switches. the rubber bit in the bottom right is what the controller actually presses down. there are supposed to be four of these, and they sit upon the interlocking pad seen in the top right and drawn below




what i was thinking is that i would solder a wire to each end of the "pad" and put some kind of component in between. i thought it was called a transistor because of this thread, but my friend said it's a relay. that's not really the issue. what i need is a component that can be switched on and off by a signal from the computer. connected between the two contacts for each of the 4 contacts, the car could be remotely controlled. the only other obstacle is the interface to the computer.

now, i've seen the DigiMeter thread where LEDs are controlled through the parallel port connector. my assumption is that, with a little help from you, i could achieve this theoretically simple, but cool, mod. so i need your help with the following: what component am i talking about? transistor? relay? how do i make the computer send the signal out? anyone who can help me will be loved and adored forever [or at least graciously thanked!]


thanks for your time
andrew/agent

 

I posted a reply some time ago for a similar problem when someone wanted help to trigger a factory bell via the parallel port. This site should help:
http://www.epanorama.net/circuits/parallel_output.html
See the simple circuit using the ULN2803 under the title Compact 8 Channel output driver. Subsitute the LEDs for relays. You might have to search (or write your own) program to trigger the parallel port.
Hope this helps.
ARM

 

ok i see that and i found the ULN2803 on jameco here

now how do i determine which relays and.. resistors? to buy?

after that, do i just solder it all together and pick/make a program?

thanks again [that guide was a very good choice, it's very, very detailed]
andrew

 

Gotta see this when it's done, that's such a great idea. I might just go buy an RC car so I can do this one haha. Post videos when you're done!

 

hey, thanks. it was just a spontaneous one. With the estimated $10-$20 that this costs for the decoder, resistors, and relays, it's a pretty cheap mod that looks like it could be a fun toy. I'm also considering mounting my [self-built] robotic arm and a video camera on it. Now that would be cool.

anyone konw about the question i asked in post #3?

 

bump

i have no idea what relays to get

 

I think relays can probably be avoided, they're more expensive and physically larger than transistors, and probably not needed.

Can you probe the transmitter PCB with a multimeter and see if one side of the switches are connected to ground or a positive voltage rail?

 

Drain the batteries alot faster too. Don't most relays take near 100ma across the coil to activate the relay? Maybe it's just the one's I've used :unsure:

 

Well since it's going to be plugged into the PC, you could hardwire the transmitter's power.

 

i don't have a multimeter :/

the physical space isn't really a problem, it would probably sit inside my computer case anyways [my computer is in a treasure chest, so i have room away from components]. what exactly do transistors do, again? i thought i would be using those after reading this thread, but noone here mentioned them until you.

 

hey guys, i really need help knowing which relay to get. i read a little on transistors and they look ok but i don't understand them quite as well as relays, so relays it is! i know to get that decoder chip, i don't know if i still need the resistors and if i did which ones to buy. after the resistor [or, if none, decoder], i solder to the relay and connect the relay to my controller as needed. then i use a program ffrom that website or make my own off of the information is gives me to send a charge out of a signal pin in the port and have a ground pin to complete the circuit. so can you help me with resistors, if needed, and relays, please

 

I personally would do something to take your PC power to 9v, and use that to power the transmitter. Then, as some said said earlier, probe for ground or 9v (it is a 9v battery, right?) and if that's the case, you can probably get away with a transistor. Actually, ideally, use a MOSFET. Just because they're sweet. But then again, static owns them. I just enjoy MOSFETs.

 

ok guys, after looking through that parallel guide for what felt like my thousandth time, i noticed the link to this page:

http://www.dakeng.com/relay.htm

the guide's pretty sturdy, but not right out, and i need some help with this image:



signal, check
1k ohm resistor, check
transistor: which leg on the schematic corresponds to E, C, and B?
relay: mostly understood. is CTC the leads for the triggered circuit [the remote control]?
220 ohm resistor, check
9v battery: uh, how is this actually hooked up? do i plug the + end in after the resistor and hook the other up to the ground?
diode: which leg is which on the diagram?
earth: the three line triangle marking on the bottom. what do i use this for?

he shows this image:

which i think i understand. there's the reed relay, the transistor, resistor, etc. he has 6 terminals and that's where i need a little more clarification. the bottom signal and ground terminals are for the parallel port. from what i understand, the CTC's are just the two ends of the circuit that exists on my rc controller [the two metal traces that the soft-button connects]. the 9V and the other ground are also there, and i'm assuming that the ground leads to the other ground so everything grounds out on the parallel port. can someone verify this?

thanks guys
andrew richardson

 

Transistor: Emitter is with the "arrow" going towards ground
Collector is going towards relay
Base is connected to 1K resistor

9V battery: Just how you said it (yes, + to 220 ohm resistor, - to ground)

diode: Anode is connected to ground, cathode is connected to the junction of the relay and collector of your transistor. On your diode, the cathode is the end with the stripe.

earth: is ground

Don't know about the CTC's though, sorry. I'm sure someone else does though.

 

well, as i kindof suspected, that was an old guide, so radio shack doesn't carry a few of the parts anymore [the important ones, the relays and silicon diodes.

*tear*

 

I'm pretty sure Radio Shack still carries the 914's, and I know they have small relays that will fit the bill as well. I just hate going there 'cause I don't like spending $1.50 for a resistor or something

You could substitute the 914 with a 4148 if need be.

 

i managed to find all the components on allelectronics.com for the diode i googled it, found a [probably old] radioshack page that gave a second number for the diode, and AE had those. i'm also guessing that this is a very smiliar relay. if i'm wrong, i'm only out about $5.

 

well, i wired it all up and got it working, mostly. i have to tinker with the reverse buttons because, for some reason, they're always on. i should be able to figure that out. i am wondering, though, if i soldered up the reed relays backwards because it takes a signal to turn the circuits off, instead of vica versa. when it's totally finished i'll probably post a picture or two and maybe a short video clip.

have to admit, though, it's pretty cool thus far.

 

looked at it some more, tested my hypothesis [signal flow was backwards in "reverse" buttons] and still am unclear. something weird happened, though, and after i turned the front ones on i couldn't switch them off. i'm thinking either i miswired something or something happened to my relays and they've gone bust. i'll see what i can figure out later

agent

 

You got the wrong relays. The ones you got are Normaly Closed, meaning that it is always shorted across the contacts unless you supply a signal to open them. You need the Normaly open ones, and that should fix your problem.