Calibrating Milone eTape

Milone's eTape is proving to be rather finicky. Per Milone's instructions, I have it installed in a 1" pipe, so that it can't stick to the sides. Readings fluctuate by up to 1/2", even with no change in water level. The eTape seems very sensitive to any sort of pressure. It needs to be suspended to give a proper reading. I neglected to suspend it during one test, and in an empty pipe, readings gradually reached 14", apparently just from the pressure on the bottom of the tape. Worse, according to this discussion, it appears that the eTape can be permanently damaged if it is submerged. That seems to contradict the Operating Instructions, which state:

The vent hole allows the eTape to equilibrate with atmospheric pressure and must not be submerged in the fluid to work properly. The vent hole is fitted with a hydrophobic filter membrane to prevent the eTape from being swamped if inadvertently submerged.

I've emailed Milone for clarification.


According to Chris at Milone, it's ok to submerge the vent hole, but submerging the connector tab will permanently damage the sensor - a detail I'd have thought would be worth mentioning in the Operating Instructions. The newer eTapes that come in tubes are sealed so that this isn't a problem. Chris says that bare eTape can be sealed by using RTV or Silicone II to completely cover the connector tab.

Prototyping a Sump Pump Controller

Most mechanical relays and switches are rated for 1 million cycles or less. That sounds like a lot at first, but if you have a sump pump that runs every 30 seconds, that's less than a year. Lowes used to sell a sump pump with a lifetime warranty. Every year, the manufacturer would mail me a new switch, and about every three years, a new pump, until they finally insisted on refunding my money.

Warranties on all the new sump pumps I looked at are awful - most are one to five years, and they expect you to mail the pump in each time. Some don't warranty the switch at all. Not keen on replacing the switch every year, and not wanting the basement to flood, I decided to build a solid-state arduino-controlled system. Water level will be detected using eTape, and the pump will be controlled with a solid-state relay. I've begun putting together a prototype:


The three-way switch is for converting between arduino controll and manual mode. The other two switches are for turning on the primary and backup pumps, respectively, when in manual mode. To the right of the switches are the relays. The heatsinks are the ones that Intel ships with Celeron processors. In the upper left corner is a freeduino, 7-Segment LED Display w/I2C Backpack, and piezo buzzer. When the local Radio Shacks closed, apparently nobody wanted the piezo buzzers, and now I'm set for life.

The switches, relays, and buzzer are attached using 4-40 screws. The arduino is attached with nylon stand-offs. The backboard is a scrap sheet of Luan. The threads on the stand-offs are just barely long enough, but it works. The mounting holes for the LED display are smaller than any screws I have, so I mounted it by bending brad nails and soldering them together on the back, to hold it tight.

The LED display will show the water level, as reported by the eTape. Initially, I'm only going to hook up one pump, so the arduino will just switch the relay on and off, as it reaches the high and low water levels. The eTape will let me utilize the entire depth of the sump, reducing cycles. If water levels go above the maximum level, the buzzer will sound. There will be a switch inline with the buzzer, to silence it.

Rebuilding a Porter Cable 18V battery

I have a large collection of 18V Porter Cable tools. The oldest are from 2010, and the batteries are starting to fail. I've heard that Harbor Freight's 18V battery uses the same cells. A new Porter Cable battery is about $40, whereas the Harbor Freight battery, with the ubiquitous 20% off coupon, is just $10.40.

Both batteries open by just removing a few screws. The Porter Cable battery is better packaged, but the layout of the cells is identical:

Side by Side

The main difference is that the Porter Cable battery has a temperature sensor:

Temperature Sensor

I left it attached to the battery connector and untaped it from the old cell. I then disconnected the leads and soldered them to the new battery - black to black, white to red.

Everything checked out:


I gave the battery a full charge. and it seems to be working well.

Unboxing the Laser Cutter

The Chinese 40W laser cutter, sometimes called the K40, has been around several years now, and prices have finally dropped below $400. After waiting for discounts to line up, I was finally able to purchase one last week for about $360 shipped. How bad (or how good?) is a $360 laser cutter?

The unit is larger than I pictured it, given the cutting size. The box is 37"x25"x16". With its weight and bulk, it was too large for me to get my arms around, so I slid it in the front door and unboxed it.


The machine itself is only 32"x20"x10". Unboxed, the laser cutter is awkward, but possible to carry. Mine came reasonably packed, with no apparent damage. It was shipped via Fedex Home Delivery from a U.S. seller, but still had Chinese labels on the outer box.

The accessories all came packed inside the cutting area. The exhaust hose is very cheap and thin. The exhaust fan looks chintzy, but is quiet and seems to run well. The water pump is an ordinary aquarium pump. The pump's box was opened, I believe to add the brass coupler in the photo below.

Water Pump

The hex fastener is too large to let the coupler screw on tightly. Since the pump is submersible, this probably isn't the end of the world. I'll probably put PTFE tape on the threads.

The cutter also came with a software CD, USB dongle, USB cable, power cable, tube of silicone, and a surprisingly nice "accessory bag", although I'm not sure what accessories I would put in it.

The cut area (300x200mm) looks quite small with all the extra parts removed. There's a lot of unused space in the power supply compartment.


You need to remove a screw to open the power supply and laser compartments. The laser compartment came packed with foam, and there were labels everywhere warning that it must be removed before operating the laser. The laser looks good.


At this point, I need to read the manual on the CD and get ahold of some distilled water and a bucket with a lid.