Elsie Kit

A low-cost L-C meter with Morse output constructed “Manhattan-style”

ELSIE is the brain child of two top QRP designers in the field today – Joe Everhart N2CX and Steve Weber KD1JV. They’ve combined talents to produce a low-cost L-C Meter that was used as the Atlanticon Kit this year at our annual QRP Forum held in Baltimore in March. (Atlanticon is sponsored by the AmQRP and hosted by the NJQRP and its members.)

The heart of ELSIE is an ATmel microcontroller that reads the frequency of a tuned circuit formed with the inductor or capacitor being measured. The controller computes the values of the component-under-test and announces the readings in Morse code via a miniature speaker. When the user presses the ‘C’ pushbutton, the capacitance is announced. When the ‘L’ pushbutton is pressed, the inductance value is announced.

Built “manhattan-style” and operated by a standard 9-volt battery, the ELSIE Kit has a bunch of neat options that are being outlined right now in the kit manual. We started with a circuit described in 73 Magazine from 1990 that used a Commodore-64 as the computing engine. But with our current technology and fascination for ingenious uses of microcontrollers, our ELSIE Meter is a flexible and easily-modified project that is differentiated from other component testers available today. The expansion features include: … RS232 serial port readout, single LED readout and frequency counting.

Because ELSIE is microcontroller-based with totally open software source code, users are easily able to make changes on their own or download new versions made available here on the project website. Of course you know that the AmQRP website is the most actively-maintained, most content-rich and educational QRP website … so, like it’s predecessor projects (PIC-EL, NorCal Keyer, Micro908 Antenna Analyzer, K8IQY Precision VXO, and all others), the ELSIE project is destined to be a classic design that can be expanded and modified to suit the individual taste of QRPers and homebrewers all over the world.

Using The Elsie Meter

Proper usage sequence for the ELSIE Meter is …

  • Power up the device with the L lead grounded and the C lead open
  • Hear ‘E’ ‘L’ ‘S’ ‘I’ ‘E’ announced in Morse on the speaker. (Version 2 software sounds the number ‘2’ as well.)
  • The unit then automatically Calibrates in about one second, then sounds an ‘R’ to indicate that it’s ready to make measurements.
  • To measure C …
    • connect the unknown capacitor from the C lead to ground
    • ground the L lead
    • press the C pushbutton
    • hear the multi-digit capacitance value announced in Morse
  • To measure L …
    • connect the unknown inductor from the L lead to ground
    • the C lead is open
    • press the L pushbutton
    • hear the multi-digit inductance value announced in Morse

Measurement Ranges

Capacitance: ~ 1 pF to ~ 1 uF
Inductance: 1 uH to ~ 500 mH
Frequency: up to 40 MHz (in version 2 software)

Version 1 Software Features

The basic features in the original/first shipments (prior to March 9th) included:

  • Inductance, Capacitance and Frequency measurements
  • Serial port reporting of L, C and F readings to a terminal program running on a PC.
    (Requires extra hardware indicated on the Enhanced Schematic, not providerd in the basic kit.)
  • Digit-serial display of the L, C and F readings to a 7-segment LED.
    (Requires extra hardware indicated on the Enhanced Schematic, not providerd in the basic kit.)
  • Frequency counter input.
    (Requires extra hardware indicated on the Enhanced Schematic, not providerd in the basic kit.)

Version 2 Software Features

As mentioned early on in the ELSIE project announcements, we said that downstream we’d have some improved features to offer ELSIE kit owners. Well, “Mr. Melt Solder” (Steve Weber, KD1JV, the kit designer) has been busily working on those new features to be ready in time for Atlanticon, and what nice improvements they are! All ELSIE kits shipped/received after March 9th contain the improved features in the version 2 software.

  • Expanded number of digits used to 8.
  • Overflow byte added to the freq counter so it can count up to 40 MHz.
  • Improved leading zero supression.
  • Added a re-calibrate function to the Frequency button. Hold the button closed for a second to re-calibrate. Initial conditions must be in place (i.e., no capacitor connected and inductor connected to ground.)
  • A small bug was corrected — The clock frequency is used in three places in the source code. We started the project using a 9 MHz crystal, but later changed over to use 8.192 MHz in the production version of the kit. One of the three references to clock frequency was inadvertently left as 9 MHz, which affects measurement accuracy.

How To Get Version 2 Software

  • If you have an Atmel programmer board (STK-500 from Digi-Key, or equiv), you can download the latest software from the link at the top of this page and program the device yourself!
  • If you are coming to Atlanticon, we’ll have an Atmel programming station set up and it’ll take 30 seconds to reprogram your chip.

Tips & Errata

  • There is a typo in the Enhanced ELSIE schematic diagram. The pin numers for segments D and E of the display are swapped. Pin 7 should be E and Pin 8 should be D.
  • It sometimes can be difficult to get started laying out a Manhattan-style project. See the high-resolution photo to get an idea how the ELSIE device pictured on this page was layed out. (The unit pictured here was wired a little differently from the final schematic in the area of the LCF pushbuttons.) Of course, your own version can take on any shape or form you desire!
  • Don’t forget to ground the L lead when power is applied to the ELSIE meter. This must be done for a proper calibration and the unit will not operate if you neglect to do this.
  • Also, don’t forget to ground the L lead when you measure a capacitor. This is the only way the front end circuit will oscillate, thus enabling the measurements to be made.
  • The socket for the Atmel micro has 24 pins but the chip only has 20 pins. Carefully cut off 4 pins (i.e., the bottom two rows) from one end before you get started. You can nip them off with a pair of sidecutters and then file the ends smooth, or just use the file alone. It doesn’t take too long or too much effort. (We supplied a 24-pin socket because it was lots cheaper than the 20-pin socket.)
  • Be very careful to not apply too much heat to the pads of the speaker when soldering that component in place. The plastic on the speaker is very thin and it melts really fast. If you hold the soldering iron on the lead too long, the heat travels up the lead and deforms/disconnects from the internal speaker element, thus rendering the speaker inoperative.

Photo Gallery

ELSIE built up in a plastic Hammond enclosure. The L, G and Common clip leads extend out to the left. (Enclosure not supplied in kit.)
Close-up of the enclosure starts showing construction detail. Note one style of homebrew pushbuttons hanging off the ATmet controller’s pins 19 (‘L’), 18 (‘C’) and 17 (‘F’).
The bare copper-clad board is first drilled with mounting holes, then oxidation is cleaned off with some emery cloth (abbrasive).
Small manhattan pads were created with an Adel nibbling tool, then attached to the base board with super glue.
The oscillator circuit was first added and tested.

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