Daniel Reetz, the founder of the DIY Book Scanner community, has recently started making videos of prototyping and shop tips. If you are tinkering with a book scanner (or any other project) in your home shop, these tips will come in handy. https://www.youtube.com/channel/UCn0gq8 ... g_8K1nfInQ

2nd Gen - Glass platen, switch/power hub

Built a scanner? Started to build a scanner? Record your progress here. Doesn't need to be a whole scanner - triggers and other parts are fine. Commercial scanners are fine too.
xylon
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Re: 2nd Gen - Glass platen, switch/power hub

Post by xylon » 19 Jul 2009, 12:54

the black edges at the ends of the glass, is that structural or is that a covering for safety?

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daniel_reetz
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Re: 2nd Gen - Glass platen, switch/power hub

Post by daniel_reetz » 19 Jul 2009, 14:06

I look forward to hearing about/trying more tape/painted edges. On my first two scanners, the edge where the acrylic was bonded sometimes cast a problematic shadow on one side, and reflected light back up on the other. I think using thinner glass with blackened edges might alleviate this slight-but-annoying optical problem.

you1
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Re: 2nd Gen - Glass platen, switch/power hub

Post by you1 » 19 Jul 2009, 15:36

Thanks for reminding me to include the edge covers.
Their purpose is:

1) Protections (me mainly)
2) provides channel (cavity) where I can fish the push button wire around the glass.

Does not provide any value to the structural integrity.

These edge covers are snug, and cover the edge of the glass perfectly.
In fact, it was a bit of challenge sliding them onto the glass (careful not to cut yourself).
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daniel_reetz
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Re: 2nd Gen - Glass platen, switch/power hub

Post by daniel_reetz » 19 Jul 2009, 15:54

Man, I love these COTS (commercial off-the-shelf) solutions you have going!

Turtle
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Re: 2nd Gen - Glass platen, switch/power hub

Post by Turtle » 24 Jul 2009, 05:47

That's a cool setup, you1, but I'm pretty concern about your power supply. It says 4.5V. The camera requires 3.15V at around 1700mA each. It might work fine now but the camera's capacitor could begin leaking after your warranty expires. :)

What you could use is a 3V or 3.15V power supply that actually reads roughly 3.15-3.2V. You might need more than 1700mA if the camera keeps shutting off or transfer speed is slow. The camera usually fails to work at 3V.

You could simplify by using one more button. Push the center and C and D closes. Hook it up so that A=C, D=B.
buttons-four.gif
buttons-four.gif (4.02 KiB) Viewed 4947 times
Or try two buttons that both buttons close if pushed in the center.
buttons.gif
buttons.gif (4.14 KiB) Viewed 4947 times
I would add a 1k resistor before the transistors. Also, if both cameras don't fire reliably you'll probably have to add two pull down resistors after the transistors.
1k.jpg
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you1
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Re: 2nd Gen - Glass platen, switch/power hub

Post by you1 » 24 Jul 2009, 07:00

Hi Turtle,

I also share the concerns that you raised. Perhaps I'm missing something and need to try everything over; however, here is what I've discovered.

During my experimentation, when I dropped my power supply to 3.x volts (using a resistor) I noticed that cameras were not turning on! So, I opted to use 4.5 volts. I'll try it again, perhaps I made a mistake with the resistor.

The transistors are another soar subject. I initially had a single 100k resistor in place of your suggested 1K resistor; however, I was unable to take a picture. In regards to transistors, a small voltage to the base of transistor should allow a higher current to travel from collector to the emitter (NPN); however, I was not able to observe such behavior.
My knowledge in electronics is extremely limited.

As for the switches...
I have a single switch on my platen handle that triggers both cameras (through the transistors).
The remaining two buttons are convenient overrides; that is, take a picture from a specific camera.

BTW.
Thank you for taking the time for reviewing the electronic component;
I was hoping someone would comment on the issues.

Turtle
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Re: 2nd Gen - Glass platen, switch/power hub

Post by Turtle » 24 Jul 2009, 11:59

Hi Edvin,

I don't know a method to drop the voltage by using a diode and a resistor as seen in your diagram. I usually use a voltage regulator. And I would think it would be easier to get a power supply that will work safely with the camera.

I can understand how you feel about the transistor issue being a soar subject. I have had no formal education in electronics and feel awful when others are in a position I once did.

I believe the two buttons version I mention previously is far simpler. But knowing that you like to use transistors, I drew up a three button circuit that uses one transistor instead of two. DC input volts is 3.6 to 5 volts. 3.15V might also work. You've observed no current traveling from collector to the emitter. That's probably because it's missing R2.
threebutton-usb.gif
threebutton-usb.gif (22.82 KiB) Viewed 4942 times

you1
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Re: 2nd Gen - Glass platen, switch/power hub

Post by you1 » 24 Jul 2009, 14:04

Hi Turtle,

Thanks again for taking the time to draw the circuit. I'll give it a try...

As for voltage drop, I was attempting to add a resistor in series.

The LED (diode) is jut for show. I wanted to see it light up when there is power :D

If I'm not mistaking, resistance and voltage in series are:

Rt = R1 + R2
Vt = V1 + V2

Assuming R2 and V2 will be the camera resistance and voltage across it respectively.
Using Ohm's law (V=IR) we substitute V1 with corresponding current and resistance and solve for R1

Vt = IR1 + V2
IR1 = Vt - V2
R1 = ( Vt - V2 ) / I

Camera spec states V2 = 3.2
My Voltage source is Vt = 4.5 at I=1600ma=1.6a

R1 = ( 4.5 - 3.2 ) / 1.6 =~ 1 ohm

What am I doing/assuming wrong?
I think I may have skipped the 1ohm resistor, because it is so small.

And as for push buttons; I'm not sure I understand how to implement a small "center" button that pushes C and D, or the spring that pushes two button on my platen handle while keeping it small. See below image.
One way to achieve same behavior would be if I used SPDT switch; however, that would require me
1) run a minimum of three wires. I couldn't find a three wire connector (male/female) at radioshack (perhaps I don't know what what to look for).
2) the SPDT switch is larger than little SPST switch that I used.
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daniel_reetz
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Re: 2nd Gen - Glass platen, switch/power hub

Post by daniel_reetz » 24 Jul 2009, 14:45

I couldn't find a three wire connector (male/female) at radioshack (perhaps I don't know what what to look for).
A 3.5mm stereo headphone jack/connector has three conductors.

Turtle
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Re: 2nd Gen - Glass platen, switch/power hub

Post by Turtle » 25 Jul 2009, 03:37

Here's a circuit that will eliminate the transistor altogether and keep a single button on the handle.
threebutton.gif
threebutton.gif (20.63 KiB) Viewed 4929 times
What am I doing/assuming wrong?
I think I may have skipped the 1ohm resistor, because it is so small.
I haven't had any success using a resistor to drop the voltage to power a large device. It might work but not as reliable.
Last edited by Anonymous on 25 Jul 2009, 03:42, edited 2 times in total.

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