Step 3: The Circuit

At the bottom you'll see a link to a pdf containing the schematic.

To trigger your CHDK enabled camera we'll be using the USB remote function. In this case we have to use it via the 'syncable' method, which is lightning fast compared to the normal USB remote.

The syncable remote also operates differently. It triggers the camera on the falling edge instead of the rising edge of the 5-volt signal. When the camera detects the 5 volt USB signal, it gets ready to take a shot, waiting for the voltage to fall to zero.

There are high-speed camera trigger circuits floating around the 'net but I couldn't find any for syncable USB. So I cobbled together the circuit below.

It uses a 556 timer IC, an inverter, a photoresistor and some caps and resistors.

The dollar store had a USB cable identical to the one my camera uses. I lobbed one end off of it, instead of wrecking the one that came with my camera.

A 5-volt power supply is needed to power the circuit. If you don't have one, pick up a cheap USB charger, or add a 7805 voltage regulator to the circuit.

The photoresistor is not on the circuit board; it's mounted on a small piece of perf board at the end of a short cable. Glue some magnets onto the back for easy alignment with the laser.

The circuit should be built first on a bread-board and tested. Once you're sure everything is working then either etch a circuit board or use a prototype board like I did. Or just continue using the circuit on the bread-board.

NOTE: OCT 2nd, 2009 There was a huge mistake in the schematic that instructable member toxoof pointed out. The PDF has been corrected.

OCT 19, 2009:  another error has been found in schematic. Arrrggggg!

July 30, 2010: Schematic revised to use photoresistor

Download the pdf here:  Schematic
<p>I have minor problem and question. My output signal is maximally 2V instead of 5V. I don't use inverter( there were none in my local electrical shop) and I measure voltage on 9 pin of timer. My question being: does inverter is somehow boosting signal?</p>
<p>I now have worked out my focus issue. There are three settings to play with to get good focus. <br>Obviously light, ISO value and other items will interfere with the final image however, the exposure time is critical to reduce blur.</p><p>My settings with the A470 to get crisp crowns are </p><p>Short Exp. Value [set] 0.00100<br>Override subj Di [On] [ 91]<br>sync delay [ set] 1100</p><p>Camera focal plane about 25 cm from the splash point.</p>
<p>I am now at a point where I can capture every drop splashing first time. I am still working on getting better focus (This will be trial and error). I updated CHDK to 1.3.0. Here are my latest steps with the A470 (Adapt to what you have).</p><p>Turn on Camera in Auto mode.<br>Turn off flash in Canon Menu<br>Focus set to AiAF<br>zoom all the way in to the impact zone<br>updated to CHDK 1.3.0 on A470 101b<br>Same dimensions and possitions in the last comment</p><p>CHDK menu<br>Enhanced Photo Operations<br>Disable overrides No<br>include autoiso and bracket [Set]<br>override Tv Type - ShortExp<br>Short Exp. Value [set] 0.01200<br>Override ISO [set] 250<br>Override subj Di [On] [ 87]<br>Left all flash menu items unset<br>Back <br>CHDK Settings<br>Remote parameters<br>ebable remote [set]<br>switch type [ca-1]<br>control mode [burst]<br>enable sync [set]<br>sync delay [ set] xxxx (xxxx ranges from 1000 to 1100 for a crown, 1200 for something that looks like a slice of tomato, 1400 for worthington Jets)<br>&lt;end of CHDK settings&gt;</p><p>I used ISO 250 with an external light source<br>changing Short Exp. Value and sync delay modifies what you capture.</p><p>I have also added a switch to the circuit to turn off the USB connector to the camera to stop me needing to pull it in and out of the camera. <br>Now I can let the camera start focusing or review the images without worrying about the trigger messing with what I am doing.</p>
<p>Here are my settings.</p><p>The laser/detector separation is 20cm on the arms. The drop comes out of a teat pipette with it's exit point being 2.5 cm above the laser. (1 inch). It then breaks the beam,</p><p>It is a 36 cm drop to the splash surface from the laser. The A470 camera is 25 cm from the impact zone (measured to the front of the lens), I set the camera to normal photos but zoomed in as far as it will optically go (Macro mode focused too close for me). Using chdk 0.9.9-964 for A470 with 101b firmware. Flash turned off (using an external light source) I have used ISO 400, 1/320 sec (which has motion blur). Also messed with ISO 500, 1/1000th (less motion blur, grainer). I have told CDHK to override the distance and found values of 9-12 seem to work (multiplier is 10). The delay POT swings from 0 k ohms to 215 k ohms. I have mine at 196 k ohms. </p><p>I found the remote trigger delay not to work in this version of CDHK.</p><p>I just updated to Cdhk 1.3.0 and I found the remote trigger delay does work and helps a lot. I can get a shot everytime. I had to manually turn off the flash as the flash override does not work. Now I have an issue with the distance override. Once I get it all working, I might get some in focus photos !</p><p>Still using milk with food colouring. Then I will move onto other things :)</p>
<p>I still have a long way to go. I can't get my delay correct but the trigger does make the camera focus and then if I am very lucky, I get an image.</p><p>I had some trouble with the A470 from Canon. If I enabled manual flash in CHDK I got one shot and then it said the battery's need replacing. I was powered off the mains at the time. </p><p>I also had a focus issue (And still do). The camera is about 25 cm from the drop and in the Distance setting in CHDK I get the results you see here after telling it that it is 10 cm from the object, else all I get is blur. I am also using ISO 500, Shutter 1/250. My drop height it approx 30 cm's. When I get it all working, I will record my settings and distances more accurately. I built the circuit on a test bread board. Fun making this and now even more fun trying to make it work :)</p>
<p>Same thing here, but controlled with your smart phone</p><p><a href="https://www.kickstarter.com/projects/969220052/camsformer-high-speed-triggeringwireless-camera-co" rel="nofollow">https://www.kickstarter.com/projects/969220052/cam...</a></p>
Hey Redrua: <br>1: Photo-resistors are much easier to location/purchase, but they aren't as responsive/fast as diodes. It's your choice what to use. <br> <br>2. The type of cap doesn't matter (except for price) as long as the value is correct. What type of cap you use depends on price/availability. <br> <br>3. 220K pots should work. Multi-turn one are preferable because you have finer adjustment compared to a single-turn pot. <br> <br>Hope this answers your question!
I have some questions. <br>First question is: In step 3 you told that schematic revised for photo resistor. I went to a electronic component store bought everything but the photodiode. Then I checked the schematic and saw that you used photodiode (sharp BS120R0F) in it. Should I use my photo resistor instead of photodiode or should I buy a photodiode? <br> <br>Second question is: I am not a electronic tech guy or something like that. I am just wondering why you used differend type of caps? (ceramic, metal film, electroylitic) when I was at component store they told me that they don&rsquo;t have ceramic ones. I thought that they all are caps and told them ok give me what you have. Their capacity are same. Now I am not sure about what I did. Will this cause a problem or not? <br> <br>Third question is : I get trimpots but they do not look like the ones on your photo and they are 220K ( they have only these). Is it ok? <br> <br>As I said I am not a electronic guy. I asked these questions to people working at shop but they said they can not give advice because they don&rsquo;t want to be responsible. And that store is the only one in this city. I don&rsquo;t care about the prices of the components (a few bucks) or price of camera (it is toy for my kid, bought for a few bucks from someone), I just want to take these photos. I just want to do it right. I will be glad if you help me. <br>
Does this cirquit triggered external flash? I have a DSLR and I want to control my external flash with this cirquit. Is that possible?
No, but it shouldn't be too hard to modify the circuit to drive an external flash. <br><br>Depends on the flash, new one use low voltage for the trigger circuit and can be interfaced very easily.<br><br>If you have an older flash, you will have to add an SCR to the circuit . It's to isolate the high voltage that the Flash's trigger circuit uses. Some older units have a couple hundred volts DC at the hot-shoe contacts.
What is SCR?. Sorry for my ignorance.
Kind of a transistor.
OMG snap we used the same background music in our instructables! XD<br>Mine is http://www.instructables.com/id/Melody-Muffs-The-Real-Mans-Headphones<br>hella cool idea btw :P
Great minds think alike! Excellent 'ible BTW.
will this work with a canon eos 350D? (digital rebel xt)
I don't think so, it's not on the list of CHDK list.
SaskView, you bewilder me.<br><br>-TheWaddleWaaddle
Can I do this with a Kodak EasyShare CX6230?
No, CHDK only works on certain Canon cameras.
ohhh... :-(
I've got one question for this. Is it possible that I could substitute the laser for an IR Led? I have a photodiode that I have used in the past with infrared Leds and it has worked wonderfully. I was thinking that a decreased distance wouldn't matter as long as the milk drop (or object) fell in between the Led/laser and the photodiode. I'm just trying to make this on the cheap and I don't have a laser but I do have an IR led, any response would be helpful. :)
That should work fine.
Thanks for the info and the speedy reply :)
Sorry, I have one more question. Would these (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&amp;itemSeq=95160176&amp;uq=634304685562081024) photodiodes work? They appear to be the same except in cost and their micro amp output (7uA [original] vs 11uA [this one]) Just want too make sure, thanks :)
That link is broken, it comes up part not found...
Oops, http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&amp;lang=en&amp;site=ca&amp;keywords=475-2863-ND&amp;x=0&amp;y=0
Looking at the specs, it should work.<br>You can check by looking at the spec sheet's graph of the 'spectral sensiivity': A red laser is about 660 nm and that falls in the middle this diodes response.
Hi there,<br><br>The part &quot;LM556CNFS-ND&quot; is no longer available.<br>Will this part from digikey suffice? &quot;296-6504-5-ND&quot;<br><br>Thankyou! I cant wait to make this project :D
Yep, that will work.<br><br>Take another look at the parts list and schematic: I've changed to a photodiode instead of a photoresistor.<br><br>The diode version works much better than a photoresistor. I've tried both, and I don't recommend using a photoresistor because it has a slow response and doesn't trigger reliably.<br><br>Cheers!
Whilst others might have made these comments else where, I have a few comments to add. <br>I built this rig and have yet to take any photos (At the last minute, I found out the batteries in my camera were flat - 10 minutes ago, before writing this .... talk about tension). <br> <br>I know these instructables are open to interpretation and doing things your own way so I have modified this a little. <br>Firstly, I didn't have magnets or a glue gun. I used glue backed Velcro. I also could not find a laser pointer like the one I wanted (where I could remove the laser easily) so I bought a laser mounted on a circuit board and then shorted out the momentary switch. <br> <br>Anyway, from the top of the rig down, here is what I did. <br> <br>I velcro'd an empty clear plastic biscuit tray upside down to the arms holding the laser. I then used a soldering iron to poke some holes in it. I use these holes to poke the particular eye dropper through that I had. <br>I used the holes to get closer and closer to cutting the laser beam that is below it. To steady the eye dropper through the hole, I used an old drink container lid and some bluetack. (I will try and post photos at some stage). <br> <br>I created a cross with two pieces of wood. Each 25 cm long, 4 cm high, 2 cm wide. Screwed in the middle to make the cross. On the end of one wooden beam, I screwed on two more pieces of wood which forms the arms. Each arm 9cm long, 2cm wide, 4 cm high. In one arm, I drilled a hole to poke the laser housing through (in my case 1.5 cm diameter). The laser fits snug and does not move. <br> <br>My laser is attached to a battery tray that holds 4x 1.5 volt AAA batteries. I shorted out one compartment so that the pack delivered 4.5 volts. I then used a soldering iron to poke a hole through in the end unused compartment and used it to put a toggle switch in to activate the laser. I placed Velcro on the back of the battery pack and secured this to Velcro on the laser arm. <br> <br>I then cut up an old milk carton and put some Velcro on this. This becomes a light guide and shield against lights from above. This is velcro'd to the second arm. Then I attached the Photodiode and leads to some Velcro and attached this to the second arm, under the milk carton. <br> <br>The laser to photodiode distance is about 20 cm's which is a convenient length. The dropper is suspended about 2 Cms directly above the beam. <br> <br>The arm was then G clamped to a vertical bar. This is about 46 cm above the plate I will be dropping food coloured milk onto. <br> <br>I then bought a 5V usb power pack with the USB female a Type cable insert as a part of the power pack. I got a cheap USB A type to Mini USB. I cut this in 1/2. I wired the USB A type end into the circuit as the power source and can plug this into the power pack. I wired the mini usb from the circuit to the camera (just like the original instructable). <br> <br>The circuit is mounted on a bread board. I used 2x temporary Zif sockets with easy release levers (18 leg) to hold the two ic's. I found some old solid core cat 5 network leads and cut them up as hook-up wire. <br>I used heat shrink over cable parts I needed to protect or wanted to stop moving about. <br> <br>This all leads off to the A470 camera running CHDK. This is behind a small piece of glass (As recommended in the instructable) and I got some further pieces of wood to cut some notches in to hold the glass up vertical (As shown in the instructable but not discussed). <br> <br>As my camera and flash both fall behind the glass, I have used a DVD cover to raise the camera and tripod to the correct level. <br> <br>I then tweaked the sensitivity pot so that the drops from the dropper trigger ever time. <br> <br>Now I just need some batteries and further tweaking. <br> <br>Wilst I did have attery power, I also discovered setting the camera to the playback mode and triggering the laser beam, causes the camera to cycle through the images. Me thinks this might have other uses !! <br> <br>Maybe setup an enterence laser to your home, someone comes through the door and a display panel cycles a picture on the camera displayed on a tv. Could be fun for things like birthdays with various images coming up on the TV. <br> <br> <br>
Excellent tips!
Thanks SaskView, <br>could this be easily set up to connect to an event counter? eg if you wanted to count how many drops went by...my application would need to count a 2-10msec break and count up to 20 such events a second....my application needs a separation of 6 m but you have answered the distance issue. <br> <br>mickyj - where did you gets the bits in Oz? <br>
Should be do-able, It's using TTL.
I obtained from parts from Jaycar and the rest from Digikey (International)
I have found my next roadblock. <br> <br>I bought new batteries, but they do not last long in the A470. Not long enough for me to get everything working. The A470 seems to drain power. I bought a power adaptor for the A470 and think I found an issue with chdk a470-101b-0.9.9-953-full. <br> <br>If I power from the mains power pack without CHDK loaded, it works fine. If I use CHDK after one flash, the camera tells me it is flat, change batteries and then it shuts down the camera. <br> <br>Still working on it ...
Using chdk 9-964 on the A470 I have found that the Override Subj. Dist. V. works. However, I have set it to zero as it zooms the camera to a place where I do not want it.
Maybe you should offer to sell ready made kits or bags of components on eBay ? I have been struggling to find all the parts here in Australia. I really want to give this a go but ... not until I have everything :)
All the components are available at www.digikey.com and they will ship to Australia.<br /> <br /> The photodiode is the only obscure part. &nbsp; Any visible light photodiode should work.&nbsp; The datasheets will usually have a graph called Relative Spectral Sensitivity.&nbsp;&nbsp; Ask for a photodiode with a range of sensitivity that includes 650 - 670 nanometers (a red LED laser's wavelength).
Hello,<br /> <br /> Yes, I contacted Digikey about 1 week ago (just before your post). There is about a 2-3 month delay on the same items I can't get in Australia. Hopefully I will get everything just after christmas. I&nbsp;will have to book mark this instrucatble and come back :)
2-3 months....Ouch!<br /> <br /> Let us know how it goes.<br />
Still waiting on all the bits :(
Did you get all the parts yet?<br />
wow, that is freaky. I&nbsp;just got most of the parts. You were reading my mind :)
Oooh... Psychic. Go me!<br />
I have finally found time to build this. I built it on a bread board and modified the laser pointer to suit my own setup. I have yet to put a frame together to hold the laser and photoresister however, I have a working circuit which I can attach to the camera, block the beam and the flash goes off. Now it just needs to be tested. <br> <br>Awesome instructable.
Thks, could you gie me a pdf file pls? thanh.thong33@yahoo.com. Thks again
I've added a link to the pdf that anyone can download. It's on step 3, at the end of the text, just above the pics.
Hey can someone e-mail me the PDF file. adamperro@gmail.com
Great job. You just let the whole world know your email. Prepare for spam.

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Bio: In December 2009 I published The Most Useless Machine Ever. 2011 formed The Frivolous Engineering Company Inc. in order to supply Useless Machines to the ... More »
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