Nuts and Volts - September 2013

Steve, thanks for the feedback!

1. There are some typos in the DC/DC converter text and schematic. The correct name is TPS62730.

2. The PUMH10 does use bipolar transistors, not MOSFETs. As for driving the camera directly, note that the pullup voltage on the camera is unknown. Some cameras can be as high as six volts.

3. Correct. The CR2032 is a lithium manganese battery with a floating voltage just above 3.0V. This is different than common lithium-ion batteries which have a voltage of 3.6V.

4. There is an error in the figure. The 1M pulldown resistor is supposed to be connected to "shutter," not "detect." When unplugged, shutter and detect are shorted together and the 1M pulldown serves to keep the circuit off. When plugged, the detect line is isolated and will be pulled up by the 10M resistor to turn on the device.

5. The choice of having a female connector on the dongle was mostly driven by the cost of packaging. Putting a single hole in the polycase enclosure is simply the least expensive option.

As a final point, the battery life can be extended by changing the inverter used in the circuit to a lower power logic family (74AUP instead of 74AHC). The new part number is Mouser #595-SN74AUP1G04DBVR. This is the part we are shipping in the kits.

Michael Wieckowski, Ph.D.

Inductor Errata

I found a mistake in Figure 10 from my induction charger project in the August 2013 issue. The current limiting resistor "R8" should be connected to [IN] which is the 4. 35 to 6. 5 volt input. To the left is a revised schematic.

Matthew Bates

Keeping Tabs on Batteries

Regarding Bryan Bergeron’s editorial from the July 2013 issue on li-ion battery tech: Next time, install the battery with a piece of paper (a paper tab), blocking one pole from connecting to the circuit. This is commonly done with LED flashlights and kid’s toys.

Phil KE3FL

Matching Tubes

I read Steve Borsher's letter regarding tubes in the June 2013 issue with much interest. I was a service tech at the Canadian national distributer for Dynaco back in the late ‘70s and serviced many Dynaco amplifiers — some of which were the MKIIIs and MKVIs.

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