i am designing a sumo robot... but i am having trouble with the ring edge detection... i am using LDR to detact the ring (i can get LDR for free) but the response is not so good... the edge is a 5cm white line... my robot can speed up from 10cm/s to 25cm/s and weigh almost 1.8 kg... so the momentum is high to stop or reverse from about 2 cm from the edge... without any supporting calculation i think if i could make the detaction faster could help my robot to stay in the ring... so can any of u help me over here...?

I have heard that the main disadvantage of LDR's is that they are slow to
react and that is OK if your sumo is slow.... But yours isn't

You could try Increasing your light source brightness.

have you tried to use a microswitch and an LDR combination? (The micoswitch as a sort of pre warning).

Alternalive would be to use a phototransistor as a detector instead of the LDR? (I think a phototransistor reacts quicker and is similiar circuit)

Are you using a microcontroller in your sumo?
Are you using an A/D converter for the LDR?

micro switch + LDR combo...?? how's that...? i have no idea... on that type of pre warning... how is the schemetic circuit...

i've tried with bright light (home white tube florecent light and even sun light) but the reaction is never close to what i've hope for...

yes, i'm using a mc in my sumo bot.... 68hc11e1... but i didn't use the a/d... it uses plenty of time to process... and eats up memory of the mc... so i op-amp comparator... the detaction is closer to real time...

do you think that you could use ultrasounds?
much better and fast.
but if you say you have the ring as a white line.....is it just white, or it also emitts light?
i would go fot the phototransistor.

i don't know that ultrasound can be used to detact white line.... cause this white line is flat on the ground (as in common sumo robot competition)... how to use the ultra sound...

i am using ultra sonic tx & rx module for opponent detaction...

the ring is flat black with a 5cm thick glossy white edge... it is just a white line and do not emitts light...

Originally Posted by kinorig

micro switch + LDR combo...?? how's that...? i have no idea... on that type of pre warning... how is the schemetic circuit...

i've tried with bright light (home white tube florecent light and even sun light) but the reaction is never close to what i've hope for...

yes, i'm using a mc in my sumo bot.... 68hc11e1... but i didn't use the a/d... it uses plenty of time to process... and eats up memory of the mc... so i op-amp comparator... the detaction is closer to real time...

I only suggested the micro switch and LDR combo because you wanted to use LDR's.

There is no specific circuit that I had in mind. I was thinking more as a compliment to the LDR..
I was not thinking of detecting the white line with the micro switch. if the sumo is approaching the edge then the micro switch would trigger as a part of the sumo goes off the edge. (just a regular logic change on an input pin)

Have you tried changing the resistor value in your potential divider / LDR
combination to get a a better threshold for your comparator?

Do you have the LDR at the top or bottom of your potential divider is the
output to be a high or a low value when it is over the black?

Would changing it the opposite way around help?
Could it be that it is being reflected when the sumo is on the black or the
white ring and only changing when it goes off the edge? (causing it to always miss the white line)?

One other option would be to slow down your sumo...
I'm out of ideas...

i think i should try to use a phototransistor... instead of a LDR... it might work... because the reflect if faster... i never thought of using micro switch... but that also might be useful... but to use that... i havechange the shape of my robot... if the phototransistor doesn't work i might try that... thankz for the idea... you are all very helpfull...

You should look at reflective IR Sensors. They're just a LED and a photo transistor packaged together in a little plastic housing. With 2 resistors a pot and a comparator you should be able put together a nice sensor that gives a digital output. The sensors can be modulated into the KiloHz range so speed shouldn't be a problem. Digikey should have a bunch of these sensors in various configurations.

Brent

Digikey sells the sensor I used and works pretty well.......... Part# QRB1114

They are fast for me, also the QRD1114 will work and is smaller, but I never found them in stock :?

Ivancho