Updated version of the cooking timer

Christmas was approaching, and I thought it might be a good idea to make a gift to someone myself rather than buying one.

Since I already had all the components for a cooking timer, I decided that would be it. However I decided to address some of the shortcomings of the first version.  These were:

• The power solution, I decided that this version would use Lithium-Ion batteries instead. This also made the base a lot smaller.
• The buzzer, I decided to replace that with a speaker and make a mechanical solution to  amplify the sound.

Since making the first version, I had already purchased the 3D printer, so I had a lot more options available to me. I could for example print in red filament, and even do multicolor printing. So another change I made was to print the switch texts (ARM/DISARM) in red.

The electronics bit remained largely unchanged, apart from the fact that instead of soldering a buzzer to the PCB I soldered wires with 2-pole connector that would then allow me to connect the speaker.

So all these changes ended up affecting the following components that needed to be redesigned.

• The base, a complete redesign was necessary to accomodate for the new battery and the USB-charging module. Since 3.3 volts was sufficient for this, there was no need to use the buck boost module. This design did need quite a few iterations to get the module seated right. The problem with the module is, that it has no real attachment points, you cannot  screw it into anything.
• The "dynamite sticks" were also redesigned to house the speaker and the actual battery. Since there was plenty of unused space there, it was a logical place to put them. The battery was put in a cradle, that then screwed into place in one of the tubes. The speaker was put in a holder in another tube with a similar screwed in place holder. 
• The display housing was redesigned to support two color printing for the labels. That meant that the housing needed to be printed in another orientation.

After these changes, this is how it ended up looking !

This time I have all the files in store, you can find the 3D prints in MakerWorld following this link, and the PCB is available from PCBWay following this link. The actual build, schematics and bill of materials is described in the original article. The only change to the BOM is the addition of the charging module, Lithium Ion battery (18650)+holder and a miniature speaker.

I even wrote a user manual for the device since it was given as a gift.

Assembly instructions

Before you attempt final assembly, test that the electronics works as intended !

After you have printed all parts, you can follow these instructions for assembly. You will need some heated inserts for M2, M3 and M5 screws, all the PCB:s and modules are attached with screws as well as all the parts are put together using screws.

1. Bottom housing

Insert 4 M3 heated inserts into the raised legs, screw the PCB into place paying attention, that the dip switches are visible through the hole. Attach the charging module to the slot on the corner of the piece, and put in place the small pin to hold it in place. You need to solder wires to the charging module as per its own instructions, one pair of wires needs from the OUT+ and OUT- terminals to the PCB, but the positive wire needs to be intercepted by the power switch. For now, simply insert a two pole connector on the red wire between the charging module and the PCB. Another set of wires need to go from B+ and B- terminals to the battery. Again insert a appropriate connector on these wires and then later another connector on the battery wires to make the connections. Make sure you use connectors that enforce correct polarity !!

2. Top Housing

Insert 4 M2 heated inserts into the corners of the housing. Do not screw the two housing together just yet.

3. Middle block

Install 4 M4 heated inserts to the bottom of the housing (thicker part) and 4 M2 heated inserts to the side. Now you can screw the Middle Block and the Top Housing together and run all the wires through

4. Display Module

Top

Bottom

Install 8 M2 heated inserts into the Top Module. Screw the seven segment display, rotary encoder and the power switch (arm/disarm) into place. You need to prepare the respective wires to connect the modules to the PCB and now is a good time to install the wires from the power switch to the charging module. The housing beneath the center block is going to be tight, so you should make the wires long enough to connect to each other in the center block area. Avoid these connections in the housing part !

The bottom part screws into the center block, and the top part screws into the bottom part after that. at this time you should have all other wires except the battery and the speaker connected. Now you can also screw the Top and Bottom housings together. There is no picture, but the knob for the rotary encoder is simply pushed into place.

Run a fake wire from the opposite side of the power switch, that will serve no functional purpose but it will be the detonator wire in the ready device.

5. Dynamite sticks and battery holder

The part on the left has slightly thicker base, install a M5 heated insert in to the middle of this part.

Install a M3 heated insert into the battery holder. Screw the 18650 Li-Ion battery holder into this holder, and install the battery. Make sure you get the polarity right ! After that, screw the holder into one of the tubes on the left side part. Now you can run the battery wires to the connector you made in step 1.

Put the miniature speaker into the tube with threads on the right side. Run its wires through the above plug and screw the plug in place so that the speaker stays put. Connect the speaker wires to the wire from the PCB.

Now you can screw the Dynamite sticks together so, that they tighten agains the middle block.

6. Caps

There are two types of caps in the printed parts. The one with the "nozzle" is going to be used for the fake detonator wire you made in step 4, and the others will cap the remaining tubes. Leave the tube with the speaker uncapped ! The caps are glued into place.

Now the Timer is ready !

So I bought a 3D printer

 So I bought a 3D printer...

During my watch winder project, I got so frustrated about printing at the library, that I decided I need my own printer. So I started studying the interweb, watched endless Youtube videos and read endless reviews.

My goals were to have a reliable, easy to use and future proof printer. After carefull market analysis, I had limited the selection to two brands, Prusa (which was what the library had) or Bambulab. After more analysis, I ended up choosing a Bambulab P1S with AMS 2 Pro, my reasons were:

• Good reviews
• Ease of use
• Good quality prints
• The AMS2 option
• a very good deal from Bambulab website !

I do not mean to say, that the Prusa would not have been able to do the first three bullets as well, but money does not grow in a tree, so P1S it was. I later learned that the probable reason for the good deal was the introduction on P2S, but that's life...

I was aware of the controversy around Bambulabs policy on using 3rd party slicers. But I am happy using Apple ecosystem products, so I figured that this is pretty much the same thing so I did not think that was such a big deal for me.

I was able to set up the printer real quick, and I was printing in no time at all. That really speeded up my work and made it possible for me to finally finish the watch winder project.

Since then I must say that it was a really good purchase. I've been using it a lot for many different things. It's good for making precise jigs. I've used it to make various spare parts and to try different concepts. But most importantly, it allows me to perfect my designs. If each iteration of a print took weeks, at some point you would settle for good enough. Now I don't have to.