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8.08.10 | Modding a projector clock
Filed under: Computer — Tags: , — Dr. Ivan @ 21:30 — Comments (0)

This is a very short and simple tutorial on how to mod a battery powered projector clock to run on power from a usual wall wart.

Introductuion

I found myself recently in need of a projection clock. I did not want to shell out too much moolah for it and I wanted to have some electronics to tinker with while I’m on vacation – perferably something with less voltage than the net standard of 240V (sorry, I’m still kind of nervous around such voltages – as probably you should too; being a medical student I have already seen my share of consequences of a slightly too liberal ). So, I bought a cheap-o projector clock running on AA batteries and a projector based around a single red LED and an LCD display in front of it.

Goals and challenges

I was not too happy with the design of the clock (since I wanted some electronics to tinker with this is kind of expected). Here were the two main shortcomings I wanted to do something about:

First of all, the clock was running on batteries. Don’t know about you, but I prefer not to buy new AA batteries every week. Expensive, environmentally unfriendly and in the end simply tiresome. The clock was running on two AA batteries, equating 3V of input voltage which is somewhat inconvenient to work with. In any case, I wanted it to run from a standard electric socket.

Second, to conserve battery juice, designers of the clock made the projector turn on if you press a button on the top of the clock chassis. It is supposed to turn on for a couple of seconds then turn itself off. I wanted it to stay on permanently.

The Plan

There are of course several courses of action to rectify the first problem. I have always loved using USB as a source of power – you get a standard 5V of voltage which is quite flexible for most purposes. That being said, I’m not willing to sacrifice any USB ports on any of my computers (nor keep them running throughout the night). Therefore I thought I could use a wall wart USB adaptor which simply down-transforms 240V (120V in America) AC to 5V DC. Then you will need one of the standard USB cables (I will be using male type A to male mini USB). From here you can either get a USB connector or sacrifice the USB cable. The latter implies that you cut off the male plug, take two wires (red and black) and permanently wire them to your protoboard. I was not too happy about this idea, so I went for the former option. This way I can still salvage the cable if in dire need. Still however – 5V will most probably fry the clock circuitry which is rated at 3V. Now, we need to regulate the voltage down to this value. However, as already mentioned this is not a particularly standard voltage, and regulators are slightly hard to find. Finding 3.3V (often spelled 3V3) voltage regulators is however much easier. This is yet again slightly too much (which makes somewhat uncomfortable), but I tested it by connecting the clock up to one of my Arduinos and it seemed to work just fine – so this will have to for this project.

So in short: We need to make a simple voltage regulator circuit and solder it to the clock’s internal PCB to power it.

The second problem (projector turning itself off) can of course be solved by taping the button to close the circuit permanently – which would be the fast and dirty way to do it. However, as sophisticated as we are (*cough*) – armed with a soldering gun and all – this is far beneath our standards. Especially when you can just solder the circuit closed. But seriously, choose whichever you prefer. You can also opt to go for an on-off switch if you wish to be extra fancy about it.

Material list

Here is a list of parts you’ll need:

  • Wire – I use solid core wire acquired at Sparkfun (link). Whichever wire you use – it is very nice to use colored wire so that you know + (standard color: red) from – (standard color: black)
  • Small protyping board – You can probably do without and just use wire, but this is much more elegant and permanent solution.
  • Wall wart USB adaptor – This can be bought at eBay for just a few bucks. It basically transforms your regular 240V (that is 120V in the US) out-of-the-wall voltage to standard type A 5V USB contact.
  • USB connectors – Any type will suffice as long as you have the correct cable for them (see next item). I am using mini USB (just because I have a wealth of them and matching cables lying around).
  • USB cable – A cable that will connect the wall wart to our voltage regulator circuitry.
  • Capacitors – I will be using one 100 uF and one 10 uF caps. You can also probably get away with just two 10 uF caps. They should be rated to a voltage above our input voltage. Anything above 10V should be safe.
  • PCT resettable fuse [optional] – You can opt to use a resettable fuse to avoid blowing you clock while tinkering and connecting all the parts together, however I did not. Choose something rated above 0.25mA.
  • The usual soldering/electronics tools – Soldering iron, solder wire, wire cutters/stripper. I was also forced to use some tape to secure the projector. If you are interested in what kind of tools I use, please visit my parts page; note however that not all of those are necessarily needed for this particular tutorial

Putting it all together

First of all, after opening the clock the projector unit (on the left on the picture below, marked with “1″ ) kept falling off, so I taped to the chassis. Furthermore, I thought that most of the wires inside the clock were far to flimsy and became unsolder when I tried to attach my wires to them (which I guess was to be expected). This prompted me to cut them off and re-solder all of them with my own wires (marked “2″ on the pic below). I also removed one of the momentary switches under the “projector” button and soldered together the broken wire they initially were meant to close (marked “3″).

internal-wiring

Now I closed the clock again threading the two wires which will supply our clock with current through the hole where battery lid would have otherwise fitted:

closed-lid

After ensuring that everything was working properly by hooking the aforementioned wires to 3V3 and GND pins on my Arduino, I started working on the voltage regulator circuit. First of all we should solder the USB connector to the PCB. The pins you are interested in are the first (+5V) and the last one (GND). I simply cut off the rest of them. However, take care not to break the required pins – especially if you are like me working on a mini USB connector – they are very fragile. When done, just solder the connector to your protoboard.

usb-conn

Further we follow the following schematic (modified from one of the SparkFun brilliant tutorials) and solder connecting the components together on the PCB:

PwrSupplSchem

It should look similar to the picture below. It should however be mentioned that I (typically) misread the datasheet for the voltage regulator and connected its pins wrong – which lead to cutting it loose and re-soldering it to the back of the PCB – which is precisely the reason for the slighly odd circuitry.

pwr-suppl

Finally, connect the wires running from the clock to the +3.3V output and ground. When all is finished, fetch your 220V to 5V USB wart. Here is mine:

200v-5v-usb

Plug it into the wall and connect it with a wire to your power supply circuit. And voilĂ !

modded-clock

Conclusion and possible modifications

A rather simple modding session. Nonetheless – it is always a pleasure to do something that is of day-to-day use just that little bit more user-friendly :)

Some further ideas: Instead of letting the projector stay on permanently or having a manual on-off switch, you could easily go for a ambient light controlled switch which would turn the projector off during the day. This was beyond my initial considerations – since my projector was running on an single LED which draws both very little in terms of current and is easily replaced. However, if you have a more powerful project with a lamp or a laser or whatnot this might help you save some mAh. Or perhaps you want to do it just for fun!

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