Author Topic: External Memory Reader  (Read 3490 times)

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Offline Captain_TunaTopic starter

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External Memory Reader
« on: August 05, 2008, 06:03:50 AM »
Hi guys it's me again :)
this time i basically want my microcontroller to read data from an external memory card/chip/anything, and also make the microcontroller change the value stored in this memory.
It has to be/have:

-quickly rewriteable
-cheap (i will only be needing a single byte of space)
-it doesn't have to be small

and, uhm...that's it. What i've found so far on the net didn't quite match what i'm searching for. I usually find some expensive memory card readers or extra-extra small chips i don't even now how to solder (because of their super small size).

:)

Offline airman00

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Re: External Memory Reader
« Reply #1 on: August 05, 2008, 06:12:14 AM »
ummm why do you need external memory? Why not just use internal memory of microcontroller ?

And can you please tell us application , it makes it easier to answer.
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Offline Captain_TunaTopic starter

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Re: External Memory Reader
« Reply #2 on: August 05, 2008, 06:40:26 AM »
the application you ask? sure i'll tell you : i wanted to make a laser tag module and later apply this module to a bot. Laser tag is some kind of airsoft/paintball, the only thing is that it works with IR (you can see my other IR-related post in the electronics section). So basically i want each magazine of the "toy gun" to have a memory which reads "30" which is the number of rounds inside it. when i press a button connected to my uC (trigger), the memory needs it be changed (it now needs to be 29 since i've used a bullet).

There must be a "memory" in each magazine, that's why i'm searching for a low-cost way to do this. I'm later going to apply this "module" to my bot so that it can search for targets and "tag" them. :)

Offline rgcustodio

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Re: External Memory Reader
« Reply #3 on: August 05, 2008, 12:35:00 PM »
i am assuming that you want you memory to be non-volatile (when you power off the data doesn't get erase). you want memory in each "magazine" but no actual microcontroller on the magazine but instead you want connectors when docking to a "gun" so that the microcontroller on the "gun" (or your robot) can communicate with the memory, i guess?

a small EEPROM might do the trick (ie Atmel 24LC256, a 64-byte EEPROM that uses I2C to read/write to the chip, http://www.sparkfun.com/datasheets/IC/24LC256.pdf) note that EEPROM have a lifespan (read the erase/writes cycle in the spec sheet)
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Offline Captain_TunaTopic starter

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Re: External Memory Reader
« Reply #4 on: August 05, 2008, 08:04:06 PM »
yea i knew that, and that's bad :)
well if they are cheap i'll just stick to them, else i might go for a small uC (has to be cheap of course). don't have time to look at it now, i'll check it out when i get back home! (have to go out now :) )

Offline Admin

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Re: External Memory Reader
« Reply #5 on: August 10, 2008, 07:31:36 PM »
sparkfun.com sells serial based SD card readers for microcontrollers . . . not that cheap . . . but you aren't going to find 1 byte memory cards unless you make it by hand :P

Offline Asellith

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Re: External Memory Reader
« Reply #6 on: August 11, 2008, 05:39:18 AM »
Why not use a counter IC? Then you could decrement the counter each time you fire. You'll need a battery in each clip and a way to interface them to your controller by means of a few contacts where you insert the clip.

Something like this will work:
http://www.fairchildsemi.com/ds/74/74F269.pdf

It's like a $1.25 on digikey. You could even get tricky and setup the circuit to reset with a recessed button. Drill a small hole in the side of the clip and put the button behind that. The button just presets the counter to 30 by pulling specific pins low.
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Offline Captain_TunaTopic starter

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Re: External Memory Reader
« Reply #7 on: August 25, 2008, 04:49:42 AM »
probably that's the best option... but having a battery in each clip is not nice :D . anyways that's not a problem, i could just put some more contacts on the clips and keep the battery in the weapon. thanks :)

Offline Iron Man

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Re: External Memory Reader
« Reply #8 on: August 25, 2008, 10:45:24 AM »
or you could just have a switch  in the magazine holding area.

they shoot their 30 some rounds

then the microcontroller says no you can't fire anymore until you take out the magazine, thus releasing the switch, and then replace it with another magazine. thus closing the switch again.

if you just want the action of changing a magazine this will work, however if you want to limit their ammo supply, you'll need a way to address each magazine.

a neat, and slightly insane addition would be wireless connectivity between team mates with displays of their positions on  HUD.

Offline Captain_TunaTopic starter

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Re: External Memory Reader
« Reply #9 on: August 26, 2008, 07:25:39 AM »
i have to document myself on the counter thing really looks interesting but can't understand much from the datasheet (just started one month ago with electronics). about the HUD thing... i don't think i'm gonna do that mainly because i want to keep it realistic, and as you know soldiers don't usually have this expensive equipment around :)

one thing i'd like to interface is a way to make the system understand when it has been missed not by much by an infrared "bullet"...

Offline Iron Man

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Re: External Memory Reader
« Reply #10 on: August 26, 2008, 10:25:31 AM »
i was just joking about the HUD thing.

will a PIR detect the IR beam, don't know if that's enough heat?

you could mount those around and read their signal for when something went near their sector or w/e

although idk if your movement might set off the PIR, you might be able to adjust the sensitivity?


you can get them pretty cheap from
http://www.robotshop.us/home/products/robot-parts/sensors/infrared-light-sensors/sfe-pir-motion-sensor.html

Offline kevinisnekkid

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Re: External Memory Reader
« Reply #11 on: August 26, 2008, 11:00:20 AM »
I don't know about sensors detecting nearby beams, but here is one suggestion. Can you put 2 beams on each gun? Have a narrow beam for your laser. And have a wide beam for proximity detection. Use 2 different colors. Then you can use color filters over your sensors to determine what you got hit with. Or maybe use blue for your beam, and IR for your proximity. It would be harder to find out the beam width of IR, but once done, it would provide a much better look.

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Offline Captain_TunaTopic starter

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Re: External Memory Reader
« Reply #12 on: August 26, 2008, 10:31:08 PM »
this could be done yeah...i was thinking about a "signal" approach to it, but not sure it could work. I could tell the system: "hey you have been missed, but not by much" when the IR receivers only partially receive a signal from other shooters. Say a standard IR bullet is 001100, and the system only receives 001. But i'm not really sure about this approach since i am not an expert about IR (maybe it can't happen, as light travels so fast, that only part of the signal is received...)

about using two IR leds (or beams) on each gun: it could be done but: i am using (or actually will be using) a lens to focus the main led so i can make it reach long distances, and if i use a non focused ir beam than this might not work at long distances, only in close combat.

about PIRs, i don't know if they could work, simply because i haven't got much information about them. Some time ago a guy mounted a PIR on a bot and he couldn't use it while moving, and it wasn't moving that fast. Ok maybe there are different types of those but i don't really know...

PS: is there a way to change the discussion's title?
PPS: oh and about using different colors...are there sensors that instead of detecting IR also detect other colors? i guess that would be very noisy though...you know, all the surroundings and stuff.

« Last Edit: August 26, 2008, 10:33:49 PM by Captain_Tuna »

Offline kevinisnekkid

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Re: External Memory Reader
« Reply #13 on: August 28, 2008, 09:59:03 AM »
To sense colors, all you need is a CdS with a color filter over it (a piece of colored glass/plastic). Although it will detect light of any color, it will show a much higher sensativity towards the color of the filter. It would give you a low/high response instead of a on/off, so you might need a pot to trim out the background light. You would probably also want to shade your CdS from overhead lights. You will need to make sure that your filter is dark enough to block light of other colors. If you look through the filter in a dark room at colored lights, there should be a big difference between the light colors. A good source for light filters is a professional camera store.

For the 2 beam idea, I was thinking of a tight beam (i.e. laser), and a controlled beam (i.e. flashlight). You could even use a small "Maglite" for your controlled beam, just replace the bulb with a LED color of your choice (maybe IR would work like that?).

-Kevin
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Offline Captain_TunaTopic starter

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Re: External Memory Reader
« Reply #14 on: August 28, 2008, 10:50:08 AM »
what do you mean by controlled beam? Won't the same problem apply? (the one i said before, won't work for long ranges)

Also another thing: cds could in fact work in case a beam strikes it, but what would happen if it passed just in front of it without hitting the cell? Because what i want to achieve is actually having something that detects beam passing near it (= near the player) as to simulate a "slightly missed" situation.

Offline kevinisnekkid

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Re: External Memory Reader
« Reply #15 on: August 28, 2008, 12:57:34 PM »
Controlled beam, would be like a flashlight. You have the reflector that partially focuses the beam, and controls the beam width. It's not as tight as a laser beam, but it's still controlled.

I am assuming you have control over the design of all the "guns" being fired.

You're right, it won't detect a beam coming close. I don't know how one would detect that. If you have the 2 beam (laser & wide) like I suggest, "close" is being struck by the wide beam, but not the laser. What kind of range are you considering long? 20ft? 2000ft? miles?
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Offline Captain_TunaTopic starter

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Re: External Memory Reader
« Reply #16 on: August 28, 2008, 08:22:48 PM »
well i'm actually considering the range the IR (focused) beam. I don't really know how much it will be though...

 


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