Gas station without pumps

2020 October 30

Whole-wheat soda bread

Filed under: Uncategorized — gasstationwithoutpumps @ 16:11

For today’s bread-and-tea Zoom meeting, I’m making my wife’s version of Irish soda bread, which is adapted from the recipe in Beard on Bread.

3 cups whole-wheat flour
1 cup all-purpose flour
1¼ teaspoon salt
1 teaspoon baking soda
¾ teaspoon baking powder
1⅞ cups buttermilk
1½ cup flame raisins (my wife only uses 1 cup)

Preheat oven to 375°F. Mix dry ingredients together, making sure baking soda and baking powder are well distributed.  Add buttermilk and raisins to make somewhat stiff, but not dry dough.  Knead on lightly floured board for 2–3 minutes.  Form into round load, slash top deeply in a cross. Bake on baking parchment for 65 minutes until lightly browned and hollow-sounding when rapped. Alternatively, test with skewer—skewer should come out clean.

Let cool before slicing.

The soda bread looks good coming out of the oven. I’ll let it cool for an hour.

2020 October 28

Analog Discovery 2 power-supply noise

Filed under: Circuits course — gasstationwithoutpumps @ 11:38
Tags: , , ,

Last night and this morning I spent some time investigating the noise on the power supplies of the Analog Discovery 2, because some students were having trouble with power-supply noise on their audio amplifiers (an inherent problem with biasing the microphone with just a bias resistor to the power supply).

I looked at the positive supply set to +3.3V using oscilloscope Channel 1, and saw a fluctuation in voltage that was not too surprising for a switching power supply (though the switching frequency seemed ridiculously low).  The power supply is specified to stay within 10mV of the desired voltage, and the voltage seemed to be doing that.

I know that some switching power supplies shut themselves off under low-load conditions, to retain efficiency at the cost of adding low-frequency ripple to the output, so I tried running the power supply with different load resistors.  I did the sampling at 400kHz and took FFTs of the signal (exponential averaging of RMS with weight 100, Blackman-Harris window).

Here are the signals:

The signals show quite a bit of oscillation without a load, but decreasing with increasing load.

Here are the spectra from the Fourier transform (removing the DC spike):

The spike around 57.2kHz is present with all loads and remains at the same frequency even if I change the sampling rate, so is probably the underlying frequency of the switching power supply.

The rather large fluctuations in the audio range are probably the result of the power supply shutting itself off when there is low current draw.  Drawing 10 mA is not quite enough to prevent this shutdown, but 27.5mA seems to be enough.

So there seem to be at least three solutions for students having problems with power-supply noise:

  • Taking enough current from the power supply that the power supply doesn’t shut itself down.  This is a rather fragile technique, as other sources of power-supply noise (such as noise injected by the power-amplifier stage in a later lab) will not be eliminated.
  • Using a transimpedance amplifier instead of a bias resistor to bias the mic.  The bias-voltage input to the transimpedance amplifier can have a low-pass filter to keep it clean.
  • Putting a low-pass filter (with a small resistor and large capacitor) between the power supply and the bias resistor.  The resistance of the filter adds to the resistance for the DC bias calculation, but not to the resistance for the i-to-v conversion.

2020 October 23

Whole-wheat sourdough in loaf pan

Filed under: Uncategorized — gasstationwithoutpumps @ 16:31
Tags: , , ,

For today’s bread-and-tea Zoom meeting, I decided to bake a sourdough whole-wheat bread in a loaf pan, mixing several of my previous recipes together.

Yesterday, I mixed

1 cup sourdough starter,
1 cup bread flour,
1 cup water,

and left it overnight covered with a damp kitchen towel.  Early this morning, I removed 1 cup of the sponge to save as sourdough started and added to the rest

1 cup warm water,
1 cup bread flour,
2 cups whole-wheat flour,
½ cup rye flour,
2 Tablespoons sugar,
2 Tablespoons olive oil,

and stirred them together using a silicone spatula.  I then kneaded the dough in the bowl, adding

½ cup whole-wheat flour.

I added a little olive oil (a tablespoon?) to the bowl and coated the ball of dough with it.  I left the dough to rise about 3 hours, then transferred it to a buttered loaf pan, where I let it rise again for about 5 hours.

I slashed the top of the loaf lengthwise and baked in an oven preheated to 400°F (set to 450°F on our oven) for about 45 minutes, until the center reached 190°F.  I removed the loaf from the pan and baked directly on the baking tiles for another 5 minutes (turning the oven temperature down to 300°F).  In retrospect, I should have turned the temperature down sooner, as the top crust darkened too much.

The loaf is a little darker on the top crust than I find optimal, but it should work ok as a sandwich bread.

The bread cut well and had good crust and crumb, but I forgot to include salt! There should have been 2 teaspoons of salt in the recipe!

2020 October 16

Sourdough focaccia 2

Filed under: Uncategorized — gasstationwithoutpumps @ 09:18
Tags: , , , , ,

I’m retrying the sourdough focaccia that I made before, changing the recipe a little.

Day 1: I started with a light sponge to rise and sour overnight. Mix

1 cup sourdough starter
1½ cups all-purpose flour
1½ cups water

together in large bowl.  Cover and let rise overnight.

Day 2: Stir down and remove one cup of mixture for new sourdough starter. To the remaining sponge, add

1 teaspoon dark brown sugar
1 cup all-purpose flour (I ran out of bread flour)

and let rise for another day.  Meanwhile, mix

1 cup olive oil
5 cloves garlic, chopped fine
fresh rosemary leaves
1 teaspoon salt

and let it steep overnight to make a garlicky oil.

Day 3 (the day of baking): Mix into the sponge

½ cup of the garlicky olive oil
2½ cups bread flour (I bought more)
1 teaspoon salt

with bread hook. Knead in an additional

½ cup bread flour

by hand, to get a smooth dough. Place the ball of dough in a bowl with the garlicky oil (turning to coat the ball with oil), cover, and let rise 3–4 hours until tripled.

Stretch dough into a sheet about 12″ by 18″ by ⅜” in a greased cookie sheet with raised sides (use the garlicky oil from the bowl to grease the sheet). If the dough springs back, let it rest a couple of minutes and stretch it out again.  Make dimples in the top surface and pour the remaining garlicky oil on top.

Let rise (covered) for an hour.

Preheat oven to 400°F (which means setting 450°F on my oven) and bake 35 minutes, until golden brown.

The focaccia in the pan shows a bit more browning at the front of the oven than at the back. I turned the pan at 10 minutes, but I should have turned it again.

The foccacia on the plate looks quite appetizing.

2020 October 10

Two maps

Filed under: Uncategorized — gasstationwithoutpumps @ 08:34
Tags: , ,

These maps seem to be red in many of the same places. Coincidence or causal connection?

Next Page »

%d bloggers like this: