Selecting a Slowcooker

Written 2015-01-24

Tags:CrockPot Cooking SlowCooker Appliances 


Slowcookers come in sizes ranging from a pint, good for fondue or melting butter, to larger than 8 quarts. Some bases can hold interchangeable pots as well. Most recipes can be scaled down, but some recipes will be limited by size, like a slow-cooked chicken. To some degree, size also determines power consumption, so you may want a smaller one for a recreational vehicle.

Removable Pots

Many older slowcookers have the pot and base integrated. This make heat transfer more efficient and smaller than removable pot designs. However, the removability of the pot makes cleaning much easier.


Some slowcookers come with an insulated base, which keeps the outside cool to the touch and makes the whole design more energy efficient.


Slowcookers tend to come in three shapes - circular, ovular, and rectangular. Circular pots seem the most common for medium and smaller sized pots; ovular and rectangular pots tend to have larger capacities. Shape really only affects selection if you're short on storage space.


At a minimum, select a pot with at least low and high settings. Avoid anything with an ungraduated analog knob. Some more advanced slowcookers sport a programmable timer, which is great for cooking recipies that need a few hours on high, then simmer on low, without human intervention.

Exploring Eventide's VR240 Filesystem, Part1

Written 2015-01-06

Tags:Eventide VR240 Audio filesystem 

The VR240

Eventide has been producing and updating their 24-channel audio recorder, the VR240, for ages. Common use-cases would be logging support calls or recording radio traffic. Two units eventually made it to my home without any tapes. One of them eventually got tore down at the hackerspace. Luckily, these units use a large(at the time) SCSI disk as a giant FIFO to buffer the tape writes. I've always been curious where mine came from, but perhaps they'll actually be able to tell me.

Disk Format

It seems the SCSI disk inside the VR240 was never meant to be removed and placed into a desktop. The disk does not actually have an MBR, but is instead divided into 1KB blocks. The first two blocks appear to be used as headers or indexing, the rest appear to have a 32-byte header and probably contain the audio. The header for the data-blocks appears to be:

Audio Formats

The VR240 supports three different formats. The manual describes them quite well, and there's some important bits of knowledge we're going to need later about the encoding in there too. Of note, independent of encoder output rate, the sampling rate is always 8kHz. Another note from the manual: "The 8-bit samples used in the VR240 actually have a dynamic range equivalent to 13-bit linear samples, but the 13-bit values are especially coded into 8-bit quantities." 86 pages in - it's G.726 u-law. So if we can organize the bytes, we should be able to snag somewhere between 16 hours and 3 days of audio.

Where is the Audio?

Assuming the disk is written end-to-end, it should be possible to play it with a raw audio player by skipping the periodic headers. But, there are some variables: So there are 20 different ways the audio could be encoded, assuming we can guess the header size, and probably 10 of them need checking by ear. Additionally, RFC2422 states "No header information shall be included as part of the audio data.", so we're on our own as far as finding out how much audio is present per 1kB block.

Thinkpad E431 Hardware Review

Written 2015-01-06

Tags:CDROM Lenovo Intel Thinkpad 

The Display

Unless the display gamut can't be calibrated out, I'm not particularly picky, but the display resolution(1366x768) is a little low for a 14 inch laptop. The 15.6 inch's DPI would be unacceptable.

The Upgradeability

The upgradeability is great! You can move from a socketed low-end Sandy Bridge i3 all the way to a high end quad-core Ivy Bridge i7. However, the separate video chipset isn't socketed, so you're stuck with either what came on your motherboard or the integrated Intel integrated HD3000 or HD4000. With an Ivy Bridge chip, you can move from 1333MHz DDR3 to 1600MHz DDR3L. With two slots, you can seat between 1GB and 32GB, although 32GB seems to require and Ivy Bridge. Also, there's a dedicated M.2(NGFF) SSD socket for providing cache, in addition to the 2.5mm SATA 3(6gbps) port.

The Pointing Interfaces

The E431 provides a trackpad and IBM red-dot mouse. The red-dot mouse works exactly as expected, except that the mouse buttons usually located between spacebar and the trackpad are missing. This means reaching to the bottom of the trackpad, or leaving tap-to-click enabled.

I'm unsure what to think of the trackpad. It has both tap-to-click and depress-to-click. It reminds me of the early core-i macbooks, except someone forgot to disable tap-to-click. Luckily, it is highly configurable.


The CDROM is so bad it gets its own section. It starts with what I believe is some sort of nonstandard integrated tray. Once ejected, the tray flops around like a pancake, with at least a half-inch of slop. It is so loose I don't feel like I can insert a cd safely into it without holding the far end up with another hand.

The axle usually only engages one or two teeth. The solution here is to spin the disk, and if it scratches itself on the tray, you need to take it out and try again.

When running, it shakes my coffee table so hard that the my X60's LCD shakes.

Overall, optical disks will be dead once everyone has fast enough internet; I only need this one to reinstall windows.

Hard Drive Tray

Another design anomaly is that the hard disk tray is mostly clear plastic. Also, the plastic comes glued to the disk.

Also, the scant bits of metal on the hard drive tray are barely grounded by two strips of EMI cloth that appear to be added as an afterthought. The metal of the tray directly drags on the EMI cloth, which will likely wear it or the underlying glue out after a handful of insertions. Lenovo even has a note about this.

Finally, the difference between the 7mm disk and 9.5mm disk slot is spent with three pieces of foam. This is a neat idea, and the only improvement I could think of would be EMI foam to better conduct and disk heat to the metal on the other side of the bay. The foam also may cut down on noise, although it will be hard to replace if ever removed, although some disk manufacturers ship a thin matching shim with their disks that serves the same purpose.


I'm not particularly enthused with the build quality - there's a distinct lack of IBM sheet-metal making up the case - more like a Toshiba than my previous IBM Thinkpad. Also, the bloatware is strong with this one, but the price was right, and I know I can drop in a newer quad-core if it ever bogs down. Mousability is my only remaining serious concern.

Rebuilding an Astatic D104 Microphone

Written 2014-12-07

Tags:Microphone Astatic Electret Ham Radio 


At a recent Hamfest, I picked up an Astatic D104 microphone. As it turns out, there are two main models of these microphones - those with an internal amplifier and those without it. Internally the crystal microphone module has an impedance around 500k to some megaohms, which works well with older vacuum-tube radios, but for newer transistor radios a lower output impedance is desired. This is where the amplifier is useful. However, my crystal module appeared broken, so I needed a replacement and opted for a modern, low-impedance electret condenser.

Parts List

Tools List

Disposables List

Component Testing

Before starting, verify each component works.
  1. Test the audio recorder using the internal or a known good microphone.
  2. Attach electret condenser to computer, referring to the manufacturer's datasheet for the wiring diagram. Use the alligator clips to connect it to the 3.5mm pigtail. Use your audio recorder to test it.
  3. Double check twinax and PTT wire using the ohmmeter

Replace wiring on the head

The D104 comes in two main parts - the head and the stand. The head contains the microphone element.
  1. Unscrew the head from the stand.
  2. Remove 4 head plate screws to reveal the crystal module. You'll need two screwdrivers, one at each end, to do so. If you're a little OCD, remove each screw at a time, and reinsert it into the bolt so that the screws and bolts remain paired.
  3. Desolder the two wires from the crystal module
  4. (Optional)remove hidden screw from neck, and clean it. This screw will connect the twinax shield to the conductive body of the microphone.
  5. Solder in new condenser. For now, make sure you connect the condenser ground to the common microphone ground.
  6. Pack with sound-insulating material.
  7. Replace screws.

Choose your own Adventure

At this point, you could trace out the wiring through the stand, add your microphone connector, and be done. Or, you could entirely rewire the stand yielding superior shielding and noise immunity over the original design. Up to you, but plenty of these microphones work without differential shielded audio feeds. Also, rewiring the base will give you the opportunity to clean the PTT switch, but I suspect it rarely gets dirty.

Rewiring the stand

Since my radio supports a separate audio ground than the digital one, and my existing base wiring only had one ground, I went ahead and rewired the base.
  1. Open up microphone base by removing three screws.
  2. Desolder all wires from wiring hub.
  3. Remove existing wire going outside of the mic.
  4. Remove flathead screw at top of tube
  5. Desolder 3-pin connector at top of tube.
  6. Remove two flathead screws from base of tube to remove lever.
  7. Remove two smaller flatheads from tube. This disconnects the switch.
  8. Remove last screw from base of tube.
  9. Remove stand tube, may be a little sticky on the base. Pull the switch out the base.
  10. Remove existing wire going up the tube.
  11. Solder control cable to normally-open pins of switch.
  12. Install twinax+switch into tube. Slide twinax and switch into base of tube. Install two small flathead screws.
  13. Install connector on twinax.
    1. Strip insulation from twinax.
    2. Lay tube on side, so you don't drop any metal into it.
    3. Use pick to unwrap shielding from twinax.
    4. Solder twinax shield to head connector.
    5. Solder two audio lines. Take note of which go to which pins noted in head rework.
  14. Pull slack twinax back through tube, screw head connector in place, double-check PTT.
  15. Route wires into base, place tube on base, install lever and opposite screw.

Assembly Testing

Testing PTT
  1. Connect PTT and PTT ground to an ohm/beeper meter.
  2. Press and hold button. Beeper should beep or meter should read close to zero.
  3. Hold button down while moving wires, reading should not change.
  4. Give them a bit of a tug, reading should not change.
  5. Release button. Beeper should stop or meter should read open circuit.
Testing Audio
  1. Connect Ohmmeter from mic pins. Mic should measure part of an ohm to a few ohms.
  2. Connect mic pins to 3.5mm pigtail with alligator jumpers, test with computer or walkman.
Testing Crosstalk
  1. Use ohmmeter to verify mic ground and PTT ground are disconnected.
  2. Use ohmmeter to verify the only two non-open pins are the mic pins.
  3. Using audio recorder, start recording. Press and release PTT several times. You should only hear the mechanical sound of the switch closing and not any pops or crackles.

Attach a radio connector

Connect up the connector corresponding to your radio. You may also need a transistor or resistor added to your PTT lines, but this is specific to your radio, not to the mic.

Apple Laptop LED PWM Frequencies

Written 2014-12-07

Tags:PWM LED MacBook PowerBook 

Although the LED on the lid latch of an Apple Laptop is a simple device, there's a little more complexity than would be expected. Since the LED is lit while the laptop is suspended, it is important that it be efficient to avoid draining the battery unneccessarily while suspended.

One trick to driving LEDs more efficiently is to use pulse-width modulation(PWM) to temporarily overdrive the LED for a short period of time, then underdrive or not drive it at all for another period of time. This works due to something called the flicker fusion, where you perceive small enough pulses of light to be a single, continuous light.

But, it's possible to see behind the curtain. When you move a PWM'd light source, the human vision system tends to see each strobe individually, like a stroboscope, but only if the light is being moved fast enough for the strobes to occur at different locations - otherwise you won't see the strobes and the pulses will blur together.

It turns out, if you move a PowerBook(6,8) and a MacBook together, you'll see that the strobes from the PowerBook LED are further apart than the MacBook LED. This indicates that the PowerBook strobes its LED at a lower frequency than the MacBook's LED. If both laptops used the same led it would be possible to estimate the duty cycle by comparing the perceived length of each strobe, but since the MacBook has a much smaller LED, the results would be skewed.