DIY Virtual Walls??

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Finally working

Postby krt7 » June 16th, 2007, 6:13 pm

I finally got back around to this project and worked out my problem. The 35kHz setting is definitely critical as stated before. My distance issue was because the oscillator was mistuned.

I have replaced the capacitor with a 1nF (1000pF) and the resistor with a 20k potentiometer.

Once tuned to 35kHz, the reception was much better.

Ironically, I have long since found some original virtual walls used, so I don't need this ciruit anymore.
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Postby sircastor » July 25th, 2007, 5:37 pm

Hey,

I know this is an old thread, but I had a thought, and wanted to bounce it off someone who knew more about electronics than I.

Could a 555 timer be used for this? All we're doing is oscillating, right?
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Postby rj5555 » July 25th, 2007, 6:05 pm

sure you can make it with two NE555's or one NE556 ( = a dual 555 ) but you won't win anything component count and price are about the same. (in my local electronics shop 2 X NE555 will cost you ?0.20, one NE556 will cost ?0.18 and the CD4093 I used costs ?0.13)
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Postby sircastor » July 27th, 2007, 12:08 pm

rj5555 wrote:sure you can make it with two NE555's or one NE556 ( = a dual 555 ) but you won't win anything component count and price are about the same. (in my local electronics shop 2 X NE555 will cost you ?0.20, one NE556 will cost ?0.18 and the CD4093 I used costs ?0.13)


I don't know too much about electronics (yet, I'm learning), but would the two timers be to oscillate the the pulse and the carrier?
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Postby rj5555 » July 28th, 2007, 5:21 pm

yes

500Hz pulse modulated on a 35Khz carrier pulse
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Postby liamfoxtrot » September 3rd, 2007, 6:22 pm

I programmed a $0.50 microchip to send the 500hz / 35 khz and it didn't quite work. I will buy another 940nm LED and see if it is a bad LED or wrong wavelength.

The chip was putting out a 28 us cycle (14 us on / 14 us off) for 34 pulses totaling just under 1 ms. Then it stayed off for 1ms and then started the pusles again.

For a true 35 khz carrier the cycles should have been 28.6 us, but the 28 us cycle is 15.7khz - I thought this should have been close enough. I could offset the calibration on the chip and slow it down 2%, but I will try out the replacement LED first.

The nice thing about this circuit is that it takes 3v direct to microchip from the batteries and there is a direct connection from the microchip to the LED and then to ground. Just two components no resistors needed:)

If the new led and clock speed don't help I will try a small capacitor at the battery connection to the microchip.

If anyone has any other comments please respond and/or email me directly. I am willing to provide the assembly code when I get this working.

Andy
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Postby Gordon » September 3rd, 2007, 8:14 pm

liamfoxtrot wrote:I programmed a $0.50 microchip to send the 500hz / 35 khz ...
Cool! Nice effort!
... I will try out the replacement LED first.
Are you aware the VW's IR-LEDs are larger than the ordinary T-1 cased LEDs (pretty sure that is true)? I don't know what mfr & P/N they might be, but I can flash a pic of the PWB that mounts the horizontal-axis LED, if that would be useful. Looks like a T-1.5 case (3/16") to me.
...3v direct to microchip from the batteries and there is a direct connection from the microchip to the LED and then to ground. Just two components no resistors needed:)
I wonder how that is done? Did you find a programmable constant-current output function in that chip which can limit LED current; and handle the power? If so, its an amazing device. If not, you may yet have to add some components, like a drver xstr with load-resistance.
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Postby liamfoxtrot » September 3rd, 2007, 10:03 pm

If you could get me information on the VW LED used that would be great.

I used a sidelooker and only hit it with 50 ma. Microchip PICs can directly power LEDs since they each limit current to 25 ma, a max of 100ma if 4 of the 5 pins are used. I only used two pins in my first attempt.

http://ww1.microchip.com/downloads/en/D ... 41268C.pdf

Any info on LEDs used and current levels used that worked would be great.

Andy
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Postby liamfoxtrot » September 3rd, 2007, 10:38 pm

I just looked up the diode in the diagram on the previous page and realized it is 880nm and had max 100ma continuous. Was I supposed to use 880nm and not 940nm?

I will buy one more of each and see if that helps.

Andy
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Postby Gordon » September 4th, 2007, 2:14 am

liamfoxtrot wrote:... Was I supposed to use 880nm and not 940nm?...
I would stay with 940nm.

I can't help you with other LED data, but I'll attach a pic that shows it (D3).

You may be able estimate LED current by studying the VWU's schematic, which is posted HERE.
I have some current levels pertaining to the three range-settings, but I could not find it this evening.
Attachments
2004_R2_VWU_mainPCA.jpg
Last edited by Gordon on July 21st, 2014, 1:02 am, edited 1 time in total.
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Postby liamfoxtrot » September 4th, 2007, 4:02 am

I think I would need the LED spec sheet to calculate the current. It appears as though at the highest setting the LED goes through just 1 ohm. This would put most of the voltage drop across the LED and the current would depend greatly on the LED characteristics. This appears as though it would have more than the 50 ma I was using at the highest setting. However, at the lowest setting, it should be flowing at less than 10 ma because of the 330 ohm resistor. So I think I should have seen some reaction at 50 ma.

If you come across actual empirical current measurements, that would be the best way to know.

Thanks,
Andy
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Postby Gordon » September 4th, 2007, 11:25 am

liamfoxtrot wrote:...If you come across actual empirical current measurements, that would be the best way to know. ...
These data, are what I was seeking:
Code: Select all
Here are a VWU'a total input-current
data... measurements taken 041220, to
define the low-battery condition
threshold(s) at which the VWU-controller
initiates commencement of pilot-LED
flashing, and to compare those data with
fresh-cells data:

 Range   Supply    Supply     Pilot LED
Setting Voltage   Current(mA)   Status

 0-3ft  2.65-2.66    25        Flashing
 4-7ft    2.66       42        Flashing
 8+ ft  2.63-2.65   142        Flashing

 0-3ft  3.1(no sag)  27         Steady
 4-7ft  3.1(no sag)  43         Steady
 8+ ft  3.1(no sag) 162         Steady

You should be able to deconvolve I_D1 & I_D2 from the total currents (U1 draws little, it can keep alive on C2's charge) to get a feel for I_D3. I am guessing I_D3 will remain substantially greater than 100mA.
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Postby liamfoxtrot » September 4th, 2007, 9:30 pm

I was looking at the schematic some more and realized that Q6 is a current limiter. If the current is too high -> the voltage at R18, R19, or R20 will increase -> until it is high enough to flow through Q6 -> which takes away from the current that goes into Q4 -> and reduces the current going through the LED. This explains why there was no dramatic change in current with a fresh battery vs old battery.

At the low setting, the D3 current has be less than 10 mA, likely less than 5 mA. The baseline low setting current is 25 mA. The remaining 20 ma is likely other circuit current drains.

When the setting changes from low to high, I don't see any other current increases. So we can attribute everything except 20 mA to the D3 current. This would end up at 120-140 mA going through D3 "on average". This LED is only on Half the time (500Hz) at half the time (35kHz). So it is only on 25% of the time. So when it is on it must be going at 480 mA to 560 mA.

If my calculations are correct, I was no where near the long range current. However, I should have been close to the low or med setting.

Can you sanity check my logic and calcs?

Thanks,
Andy
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Postby Gordon » September 5th, 2007, 1:50 am

liamfoxtrot wrote:I was looking at the schematic some more and realized that Q6 is a current limiter. ... This explains why there was no dramatic change in current with a fresh battery vs old battery.
Exactly! But, even with that clever regulation, the beams' radiance falls quite a bit.
At the low setting, the D3 current has be less than 10 mA, likely less than 5 mA.
Some quick hen-scratching agrees. I got <4mA to 5mA>.
The baseline low setting current is 25 mA. The remaining 20 ma is likely other circuit current drains.
Remember, you have D2 drawing a fixed current of approx: <12 to 18mA>; then add about 3mA for the GRN-LED!
When the setting changes from low to high, I don't see any other current increases. So we can attribute everything except 20 mA to the D3 current. This would end up at 120-140 mA going through D3 "on average". This LED is only on Half the time (500Hz) at half the time (35kHz). So it is only on 25% of the time. So when it is on it must be going at 480 mA to 560 mA.
Wild! Isn't it?
...Can you sanity check my logic and calcs?...
Looks like you're on the right track!
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Postby 1oooop » June 19th, 2008, 3:46 am

is it okay if I make a PCB of it? it's kinda the thing I do on weekends... I'm only getting permission because... that's kinda what I do B4 I make a PCB...
[update]
well I alrdy did the schematic and the board
Attachments
V-W.TIF
a low res of the PCB... copper side
V-W.TIF (1.69 KiB) Viewed 7745 times
PCB.JPG
the black things are wires...
PCB.JPG (62.09 KiB) Viewed 7725 times
circuit.JPG
circuit.JPG (20.74 KiB) Viewed 7727 times
IDK what to say about this...
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Postby yoshihiro » September 30th, 2008, 3:16 pm

Hi, hmm... i don't really know how does this work. maybe i newbie. i try the vw on my 560 it does not work, and when i check the IR with my camera the IR doen't blink.. can anyone help me?
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newbie help

Postby misha680 » October 1st, 2008, 1:12 am

Hi, I want to build such a virtual wall. I am a newbie but very willing to learn. Here's what my take is on what I need (with links) plus two questions. Could anyone please check to see if this is correct and perhaps suggest something about these two questions? I'd very much appreciate it.

Thank you guys
Misha

1 x 4093
http://search.digikey.com/scripts/DkSea ... 4093BCN-ND

1 x BC547
http://search.digikey.com/scripts/DkSea ... e=BC547-ND

1 x SFH482
http://search.digikey.com/scripts/DkSea ... 75-1467-ND

1 x +5V power supply

1 x 79L05 --- what is this, do I need it if I use a voltage-regulated power supply (wall wort) that is 5V?

Resistors:
22K
220 (ohms?)
1K8 (1.8K) --- or is it 1K per later schematic?
18 (ohms?)

2x 100n capacitors
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Postby yoshihiro » October 3rd, 2008, 11:27 am

i wonder do anyone can help ?
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Postby Gordon » October 3rd, 2008, 3:13 pm

yoshihiro wrote:...when i check the IR with my camera the IR doen't blink..
Your eyes (and probably the camera too) are not able to respond to flicker rates above 24 Hz. That is why you sense a movie to be continuous, even though it is created by low-frequency flashing of individual images (images on a strip of film) onto the movie screen! Each film-image moves into the projector's film-gate, halts while being projected, then moves out, at 24 frames per second, or faster (for slow-motion).

For best results, you must use an oscilloscope to test a VWU's carrier-rate & modulation-rate. It might also be possible to use a digital-counter on each oscillator (to check its frequency) prior to merging their outputs

One other thing that may make a 5XX-Roomba a poor sensor for this DIY-VWU is: I think it was vic7767 who reported that 5XX models may not reliably respond to the 4XXX-model's IR sources' signals. That warning may have been for the hand-held remote-controller, and not a VWU. I can't say for certain--I have little interest in this topic, so I don't pay attention! :-)
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Re: newbie help

Postby Gordon » October 3rd, 2008, 3:49 pm

misha680 wrote:Hi, I want to build such a virtual wall. ... Could anyone please check to see if this is correct and perhaps suggest something about these two questions? ...
Sorry, I can't spend much time on this "checking". So, what follows is not a complete critique of your post, but only a few comments about obvious items I noticed.
1 x 4093...
1 x BC547...
DigiKey links for those two look reasonable.

This LED, SFH482, appears to be an 880nm wavelength device, and its in what may be an expensive metal jacket. You need a 940nm LED.
..."79L05" --- what is this, ...{?}
That, looks like a typo, to me. It should be "78L05"; which would make it a +5Vdc regulator.
...do I need it if I use a voltage-regulated power supply (wall wort) that is 5V?
You would not need it IF you truly use a five-volt power supply. I suppose 5Vdc wall-warts ARE available with regulated output voltage, but I've not noticed any that come with domestic products. If you have the supply you intend to use, just plug it into the mains and measure its no-load output voltage to see if it is greater than, say, 1.1 * 5.0V = 5.5V (for a +/- 10% regulation).
Resistors:...{&} ... capacitors
Sorry, I can't run through those values for you. But, I would suggest you breadboard the oscillators with variable timing resistances (multi-turn trimmers, in place of fixed resistors, two places). Set them to the ckt's nominal values, and adjust as required to seek optimum frequencies. Afterwards, measure the resistance of each trimmer and determine whether a single, standard, fixed resistance can be substituted. You might have to parallel two values to get the size you need for each timing resistance!

I don't know how critical the carrier & modulation frequencies are; and, whether caps & resistors having ordinary tolerances on their nominal values, provides a good chance of success. You will either have to find this out for yourself, or depend on another member--who has been through a DIY-VWU build--to advise you.
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