The Pac-Man Desktop Clock!
Back in 2015, Raw Thrills made a pretty cool desktop clock featuring Pac-Man and the ghosts. This LED pixel clock had animations was commonly found for about $40 on sale.
Clock in Action - https://www.youtube.com/watch?v=2MTn2QNU2-o
There were two main complaints with the clock..
- It was desktop style only, it's form factor did not lend to being directly mounted on a wall and
- It lost it's time whenever powered off (and drifts pretty badly even when continuously powered)... so pretty much was guaranteed to always have the wrong time.
The good news is, the unit was originally designed to have a RTC (real-time clock) and battery, but these pieces were costed out before production. According to Josh Sharpe at Raw Thrills, prototypes were also intended to have sound, but sound had to be removed when they couldn't get it working reliably on the production hardware. When costing out the RTC, the PCB was not changed, they just removed the components making it easy for us to add the functionality back!
Adding the RTC back in as a mod was discussed on the Pinside.com forum (Thread Link) and members submitted their findings on adding the required components. Member empty-m even linked the parts he used from digikey.com making it easy to ID what you needed (Post Link). But ironically, most must have found it so simple that no one bothered to document the process completely. Well, I figured that wouldn't do, so I'm making this post :)
Parts needed:
Here are the items as identified by empty-m - These have been verified to work. Others can be substituted, but you're on your own there :)
- Timekeeping chip DS1307ZN+T&RCT-ND (Digikey Link)
- Crystal 535-9033-1-ND (Digikey Link)
- Battery holder BC501SM-ND (DigiKey Link)
- CR1220 Battery (DigiKey Link)
When I sourced this for my own kit, it cost me $5.86 +shipping.. so this is cheap :)
Tools needed:
- Small Phillips Screwdriver
- Plastic Spluger Recommended (Found in most phone repair kits) - Can use a simple credit card if you have nothing else
- Soldering Gun, solder, flux
- A pair of tweezers is recommended - used for for placing/holding SMD components
- Magnifying glass, loupe or equivalent recommended - used for looking at tiny SMD joints
- Flux-remover or Isopropyl alcohol - used for cleaning up solder flux
Experience needed:
Moderate - This job is actually really straight forward, but it does require you to solder very tiny SMD components. If you have never soldered before, this maybe a tall order for you! If you have SMD experience and tools - this is a piece of cake! If you are comfortable doing through-hole PCB soldering, you can hack this simple SMD job
Modification Step by Step Guide
1. Unplug the clock and take to your bench or work area
2. The front tinted plastic must be removed. It is held in with dabs of hot glue in the four corners.
To remove, start in the middle and pry your plastic spluger or credit card in the gap between the case and front screen. Get behind the plastic and just work your way along the edge towards the corner. The screen will easily bow and lift away from the case. Just be gentle and avoid bending the plastic to where it would snap. The hot glue easily gives way without heat or extra effort needed.
Once free, set the plastic screen aside where it won't get scratched.
3. Remove the 4 visible Phillips screws from the back of the unit and keep the screws where you won't lose them.
4. Using your screwdriver or another thin stiff object, push the screen out of the case from the back by pushing through the screw holes in the back of the case.
The screen is held in place only by friction and the hot glue that held the front-screen in place. Just push gently through the holes, trying to evenly advance the screen forward until it comes free of the case. Holding the case at an angle so its supported, but not blocked at the front is helpful to pushing the screen out.
Warning! The screen is attached via wires to the PCB which is still attached to the case, so it will not come out completely. Just separate the screen from the case enough you can access the PCB
5. Move the screen away enough so you can access the four Phillips screws holding the PCB board in place. Remove the four Phillips screws and set aside with the other screws you removed previously. They are all the same type.
Once free, set the case aside and leave the screen face down on your work surface where you can easily access the component side of the PCB.
The three places of interest on the PCB are the spot labeled U3 which is 8 pads in a square shape, Y2 which is 2 pads side by side, and the battery BT1 with two pads.
Now the fun soldering part!
I am going to assume most people doing this are not SMD experts and don't have SMD specific tools. I'm documenting this using normal through-hole tools. I am not a SMD guru - there maybe other ways you may want to do these steps, I'm just giving you one way. I used a Weller temperature controlled iron at 610F with a chisel tip, and paste flux. I also use spray flux remover which allows me to clean up flux easier.
Some tips
- Magnification is key! Always use magnification to see what you are doing
- Flux is sticky and helps hold parts in place. Putting flux on the pads not only helps your solder flow, but helps keep your part from running away on you
- If you feed solder directly to the joint, you don't necessarily need to put flux on the pad before soldering. If you pre-load the solder to your tip, the flux will be burned away, so put flux on the joint when using solder that was pre-loaded on your iron's tip.
6. Install the clock chip at U3
Prep the 8 pads at U3 by covering the pads with liquid flux or flux paste, this will help your solder flow, and helps keep the part in place.
Using tweezers, toothpick, or other small tool, place the 8 pin chip on the pads at U3. The small dot on the chip denotes pin 1 which should be oriented next to the U3 label screen printed on the board. Reposition as necessary to get the chip's legs aligned on the solder pads. Use your magnification tools and get it lined up correctly.
Clean your soldering iron tip, then get a small blob of solder on the tip of the iron. While holding the chip down in place with your tweezers, briefly touch the soldering iron to the intersection of the pad and the chip leg. The solder should quickly wick from the iron and flow to the leg and pad. If the solder didn't flow, try again holding slightly longer. It should wick in under a second - if not, make sure your part is flat and you are making contact with the pad and leg.
In the photo above, you can see I used high-temp tape (the orange tape) to help hold the component in place so I wouldn't have to hold the part in place while trying to tack the first leg.
Once the first leg is soldered, and you are happy that the component hasn't moved and all the other legs are still aligned. Solder the rest of the legs the same way. Get a dab of solder on the iron, touch to leg and pad until solder wicks up to leg.
Alternative soldering methods include holding the solder at the intersection and touching the iron to the joint, or "drag soldering" where you get a mass of solder on the tip and continuously drag the tip over the pad/leg intersection. Youtube for your favorite SMD soldering advise :)
For such a small chip, I found both the pre-loaded tip and holding the solder across the joint effective. Use your magnification tools to make sure the solder wicks up into the joint and that your legs are all well connected to the pads.
Once you are happy with the soldering. You may want to clean up your flux before placing the other components. Using flux remover or simple 90%+ isopropyl alcohol flush the area and wipe away any flux. A small brush or q-tip helps. Blow out any excess fluid and check your work with magnification before proceeding.
7. Install the oscillator at Y2
The small oscillator crystal is a cylinder with two legs. The part can be installed in either orientation, you just want to make sure it fits and doesn't get obstructed by other parts. The legs are very short, so I opt'd to install it vertically, then laid it over the clock chip we just installed.
Prep the two pads at Y2 with solder. Heat the pad and add solder to the pad to create a small mound. Just enough to create a small pile - not a mountain. Do this for both pads.
Holding the crystal in tweezers, position it so it stands upright with its two legs touching the pads. Using your soldering iron, heat up the pad (which is loaded with solder) and let the leg of the crystal drop into the mound. Quickly repeat with the second pad so that the legs of the crystal are both secured into the solder on the pads. If secured, lean the crystal over towards the U3 chip and make sure the legs do not short anywhere.
Again, access to the area is tight, so you may want to clean up any flux before proceeding. Use your flux remover or Isopropyl alcohol.
8. Install the battery holder at BT1
Place the battery holder so its legs line up with the two pads for BT1. It should be oriented so the open side of the clip is on the side furthest from U3.
With these large clips and pads (compared to what you did on U3!) you can solder these legs anyway you like. I held the clip in place and held the solder on the joint and heated the joint with my iron. Make sure your solder wicks between the leg and pad.
9. Clean up any flux and inspect under magnification.
Using your magnification, check for any remaining flux reside, clean if necessary so you don't have any paste or baked goo left around your parts. Inspect the soldered joints and correct any by reheating if necessary or removing excess if you have any solder bridges. Make sure all legs are connected and you have no shorts/bridges.
10. Install the Battery in the battery holder
Simply slide the battery in from the open side and under the brass lip. Get it under the lip, then the open end will snap into the holder when the battery is pushed down.
11. Once you are confident the PCB is dry of any fluids used to clean it you can bench test your work.
Just make sure the PCB isn't contacting anything to short, plug in the 12V transformer, and confirm the unit powers up.
Once powered, use the buttons to set a time on the clock besides the default 12:00. Just set it to 12:05 or something. Then unplug the clock from the wall. Wait 2 minutes, then plug the clock back in... it should be showing 12:07. If it is (or later..) your did it! It works! If it shows 12:00, the RTC feature did not work and you should re-check your soldering.
12. Remount the PCB to the case using four of the screws.
Reinstall in the same orientation you found it. The power connector on the PCB should make sure you have the correct orientation of the board. The component side is towards the back of the case, and the two power wires feed around the PCB at the bottom edge.
13. Feed the screen back into the case.
Again, it is just friction mounted, no fasteners. Just feed in evenly. The hot glue from the original install helps create some friction.
14. Reinstall the front plastic by simply pressing into place.
The original hot glue should still be there and be sufficient to hold the panel in place. If not, add a dot of fresh hold glue in the corners to secure it.
That's it! Enjoy a clock that keeps the real-time!
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