Virus outbreak life hacks

Vegetables in 4-6 days, just add water

Growing bean sprout

While doing an inventory of my food supply, I came across some mung beans I bought about 10 years ago.  So I grew some bean sprouts from following this website. It is very nutritional and a low effort alternative for fresh vegetable during a food shortage.  I use the webbing from a pack of garlic to use as the mesh and tie it to the bottle with some solid wires.  I soaked the beans overnight and then rinse it twice a day.  Other than that, it requires very little efforts.  I had to stop after 4 days when the bottle was getting too full.

Stir fried noodles with bean sprouts

Here is one recipe for a stir fried noodle.

Egg noodles from scratch

Ingredients: 1 egg, 1/2 teaspoon of sodium carbonate, flour and water.
Tools: hands, pasta machine, measuring cup, flat surface e.g. baking pan.

Sodium carbonate (Na2CO3) can be made by heating sodium bicarbonate (NaHCO3).  It is also available as washing soda, however I don't know if they are food grade.

https://cooking.stackexchange.com/questions/9072/what-flour-and-technique-do-i-need-for-hand-pulled-noodles

Without sodium carbonate it's possible to have hand-pulled noodles with any flour. The downside is you will have to knead the dough for 45 minutes and leave to rest for 2 hours until you can start pulling your noodle strands.

The alkaline dough also help to discourage Salmonella, but hey you are going to boil the noodles at some point anyway.

1. Add 1 large egg, fill water to 1/2 mark, add 1/3 teaspoon of sodium carbonate.

Egg,, water and some sodium carbonate

2. Top it up the same measuring cup with white general purpose flour to a bit above the 2 cups mark. Why wash when you could use the same cup?

Add flour to same cup

3. Stir it around with a spoon until all the liquid is absorbed.

Stir a bit

4.  Pour contents into a surface.  I use a baking pan to contain spills. 

Lumpy mix from cup

5. Knead the dough until your hands  are clean.  It is a very tough dough, but it is a good exercise.

This is the time to stop

The clean up isn't too bad.  Leave the pan for now as you'll need it later.

Now it is time to clean the cup

6. Store the dough in a container and keep it in the fridge for about 3 hours and let it "rest".  Make sure you wash your hands after this as the dough is alkaline.  

7. I roll the dough with my manual pasta machine starting from the thickest setting.  I also trim the rugged edges and patch up holes in the dough.  Go one setting at a time to reduce the thickness of the dough sheets. Trim the length when the sheets gets too long.

This dough can be used for making wonton wrapping.

8. Cut the dough with the attachment.  Here is the finished product.I don't bother adding dry flour as the noodle is not sticky.

9. At this point you can put it in boiling water and it cooks in a minute.  Rinse under cold water to stops the cooking.  The noodle is very chewy.  Serves 4-6. The stir fried noodles was done with 1/4 of the dough.

10. I put it in a plastic container and freeze it.  I put a layer of food wrap between servings so that they don't freeze into one lump.  It take less than 2 minutes to cook in boiling water from frozen as there is no need for defrosting. 

Flat hook for DIY mask

I made a HKMask for personal protection.  I am not a arts and craft person, so I had to make do with what I have.  I modified the design as I don't have any thin elastic bands.  I do have a lot of fat ones from my grocery.

I use the I core from old transformer to make a flat hook and a AWG10 solid wire (household wiring) for the loop. The rubber band is very strong, so it is important to have the right cord lengths for comfort and fit. I crimped the 2mm paracord gently during length adjustment.  Once the adjustment is done, I crimped tightly to hold it in place.

DIY flat hook

Hook material: stamped I/O bracket cover for a cheap PC case or transformer cores

STM8 Timer - servo controlled water valve

The motor in the submersible pump I was using has started to rusting after a year and a few months. The rust stops the motor from spinning until I hit it with a high enough voltage which eventually exceeded the power supply I was using.

Pump motor is rusting

I ordered a couple of replacement pumps, but they are probably stopped somewhere between China and the post office due to the virus.  I have decided to go for a different approach.

I  made a servo controlled valve to control the water flow from a siphon.  This simplifies the overall design by removing the pump at the source and reduced the wring needed.

Top view of assembly

I used a Tower S9 micro servo mounted in a cut out dental floss case with a couple of M2 screws.  I used a cheap metal air valve, but it seems to work okay so far for water.  It is held down with 3 L shaped bracket with a couple of screws. The brackets are made out of the left over bits from the case. The servo arm is coupled to the handle with a 'g' shaped metal strip from a transformer.  The valve side is loose enough to allowed it to move to accommodate for minor misalignment.

Side view of the assembly

Two large holes are drill on the side of the case for connecting the tubing.

Timer Aux power supply 

There are a few modifications needed on my timer project for driving the servo.

• R2 is replaced by 2.7K while R7 is replaced by 8.2K.  This sets the output to 5V
• D3 is removed. The 5V output on J4B is now always on.
• J6 is installed.  The /EN signal is used for driving the servo

/EN (PD3) is used as PWM for driving the servo

The 5V, GND, PWM signal are routed to a 3-pin connector for the servo.

I used TIM2 for generating a 50Hz PWM signal for controlling the servo.  TIM2 is disabled after 1 second when the servo is in the "Off" position.  This powers down the servo and prevents the annoying rattling in some cheap servos.

Fixing my Weller WESD51 soldering iron - quality not found

I went to the only local electronic part store eons ago to buy replacement part for my older soldering iron. It was a decent iron that lasted such a long time that the store no longer carry the replacement parts.  I bought the WESD51 as it was on a back to school sale and Wellers parts and accessories was easier to find. It was a lemon. Ironically the serial number happens to be 0404 (Quality not found!?)

4 hidden screws under the rubber feet

Right from the start I had a lot of issues with the iron not reading its temperatures correctly. I thought it was a connector issue, but later I found that it was a manufacturing quality problem.  They change a PTC fuse into a larger package (green 2X2 at top of PCB) but didn't do a good job of touching up the soldering on the mismatched footprint.  So I had to fix it up in the first few months.

Control PCB

A trimpot has limited cycles, so personally I wouldn't use it for a temperature control knob. It did last a very long time, but obviously not long enough vs the rest of the iron.  A few months ago,  the temperature setting started jumping beyond my set point due to wiper contact issues. I knew I had to repair it.

PCB back side

As I was opening it up, I found out that they didn't do a proper crimping job on the AC leads of the power transformer as they tried to crimp a tinned wire instead of bare wires!?  Solder is soft, so eventually the wire came loose.

Poor crimp job

Here is the cheese knob for the trimpot.  It was held together with a self tapping screw. I had to put in some hot glue to hold the screw.

Cheap plastic knob for the temperature control

 I ordered the smallest 10K linear potentiometer I can find and they arrived today.  I couldn't find any 2K pots.  Since it is to provide a 0V to Vcc to the ADC. The increase in source impedance could affect the ADC result. One way to fix it it to wire a 0.1uF cap from wiper to Gnd, but that is not needed here.

They are not the greatest quality, but I got a bag of 5 for cheap. They came with washer and a nut.  I use a pencil to trace the outline of the washer on the PCB and milled out a notch for the locating pin.

Modification to the PCB

I mounted the pot onto the PCB and soldered the pins to the existing pads with wires.

Pot connections

I had to remove a bit of the material in front case to clear the mounting hardware for the pot.

Making room for the mounting hardware

I use a reamer to enlarge the hole, so that the PCB can be mounted flush.

Old Radio Shack reamer

It ain't pretty as it is soft plastic. The hole is hidden away by the knob.  The shaft is barely long enough.

The big hole I made

I broke off the cheesy plastic off the knob.  I got some cheap plastic knob from China that is small enough to fit inside the cavity.

Temperature control knob

It wasn't tall enough nor wide enough, so I had to improvise.  I melted about 1/2" of hot glue stick with my hot air tool set at 120C in the cavity.

Hot glue to the rescue

I pushed the plastic knob into the molten hot glue and wait for it to set.  I filed down the knob so that it is flush.  I added some extra hot glue for support on the sides as well.

Improvised knob

One of the things I did to prevent the plastic mounting post from splitting was to use a piece of cable around it.  I wish they would use threaded inserts.

STM8 LED Clock - Part 2

Go to Part 1

The regular AT-cut crystal has a temperature variation that can be modeled by a cubic equation. Variations from the ideal angle produces the following curves centered around 25C.

AT - cut frequency-temperature characteristics.

If the temperature variation is small enough, then a regular AT-cut crystal might be good enough.

e.g. home with heater during the winter set to 21C and air conditioner set to 25C for the summer. The temperature variation is roughly 4C.

 For a wide temperature range or lower temperature dependency, you might want to use a TCXO (Temperature compensated crystal oscillator).

There are a few  ways of making an accurate clock out of an oscillator:

1. Use an external accurate clock source and/or resync. the time e.g. GPS or internet time
2. Try to adjust the clock frequency of the oscillator by changing the load capacitance. This is difficult and the adjustable range might not be enough.
3. Try to compensate for the tolerance by changing the frequency divider.

I am using the last approach as it is the least expensive and provide a finer repeatable adjustment than what is possible a trimmer capacitor.  The CPU clock is divided down to generate IRQ for the software real time clock.

In my Timer project, I used a hardware timer set to overflow every 60,000. By changing this value,  I can tweak the IRQ by ~ 1/60000 which should be good enough for +/-0.72 sec/day accuracy after calibration. 

This time, I generate a 20Hz IRQ and further divide down the frequency to 10Hz for the RTC using a 24-bit Numerically Controlled Oscillator (NCO). The NCO allows for very fine frequency.adjustments.

The 3 lines NCO code is actually much simpler than the firmware that would be required to extend the hardware timer divider beyond 16 bits.

DDS Code

So far I have calibrated the clock by simply comparing when the clock changes vs https://time.is/ - whether it is faster or slow and by using a binary search algorithm to find the value. This doesn't require any additional coding or equipment, but it takes a bit of time.

The latest calibration is less than +/-1 sec/month after 7-8 turns of such adjustments.  I measured 1 second difference after 4 weeks 6 days.

Additional Reference:

• https://www.electronicdesign.com/technologies/analog/article/21795717/fundamentals-of-crystal-oscillator-design
• https://blog.dan.drown.org/rtc-comparison/

User Interface

The clock and display time:

The arrows key switches between the time and date display.  The date display uses a different format to distinguish the modes.  The 7 segment LED can only show a limited set of characters and have to make the closest approximations. 

e.g. Th(ursday) 16 Jan is shown below.

The user interface is still work in progress as the display is very limited. Here is how to set the time.

How to set time

Alternately, Hold the Menu for ~1 second to exit the setting mode.

Go to Part 3 for my new alarm clock.