Backcountry Logger Bill of Materials
The first Backcountry Logger prototype has gotten a very positive response from everyone I’ve showed it too, so I’m toying with the idea of making a few and selling them. I put together a bill of materials to estimate the cost, using the newest “shrunken” v3 prototype that’s designed but not yet built (still waiting for PCB and parts to arrive). As designed, the BOM cost is $32.01 each for quanity 100. That doesn’t include the PCB itself (probably a dollar or less for that quantity), the cost of assembly, or a case. For a quantity 1 prototype, the BOM cost is $37.20, but that assumes acquiring some parts as samples/free that aren’t for sale in individual quantities.
In addition to being smaller, the Logger v3 actually has more features than the v2 prototype shown in the photo here. The features require additional parts that increase the cost:
- $4.95: external EEPROM memory (allows storing more data samples and at higher resolution)
- $2.76: voltage booster/regulator (necessary because v3 uses a 1.5V AAA battery instead of 3V CR2032 watch battery)
- $4.58: vibration sensor (this is a totally new feature I added, to detect when you’re in motion and attempt to count your steps)
To build the v2 design, you could omit all those parts and lower the BOM cost to about $20.
The cost could likely be lowered further by searching for the cheapest component suppliers (I just used Digi-Key for everything), and by tweaking the design to use fewer and cheaper components.
| Quantity | Part | Purpose | Supplier | Price @ 1 | Ext Price @ 1 | Price @ 100 | Ext Price @ 100 |
| 1 | ATmega328P-AU | microcontroller | Digi-Key | $4.87 | $4.87 | $3.06 | $3.06 |
| 1 | MAX1675EUA+ | voltage regulator | Digi-Key | $5.73 | $5.73 | $2.76 | $2.76 |
| 1 | M24M01-RMN6TP | EEPROM | Digi-Key | $6.75 | $6.75 | $4.95 | $4.95 |
| 1 | BMP085 | pressure sensor | Digi-Key | $3.81 | $3.81 | $3.81 | $3.81 |
| 1 | UG-2864HSWEG01 | 128×64 OLED display | wide.hk | $7.99 | $7.99 | $4.70 | $4.70 |
| 1 | CCV-084B16 | buzzer | Digi-Key | $2.36 | $2.36 | $1.96 | $1.96 |
| 1 | SQ-SEN-200 | vibration sensor | SignalQuest | N/A | $0.00 | $4.58 | $4.58 |
| 1 | CFS206-32.768KDZF | crystal oscillator | Digi-Key | $0.28 | $0.28 | $0.16 | $0.16 |
| 1 | UP1B-220-R | inductor | Digi-Key | $1.38 | $1.38 | $1.06 | $1.06 |
| 1 | MBR0520L | Schottky diode | Digi-Key | $0.63 | $0.63 | $0.20 | $0.20 |
| 3 | B3FS-1010 | tactile switch | Digi-Key | $0.65 | $1.95 | $0.47 | $1.41 |
| 1 | 2466K-ND | AAA battery holder | Digi-Key | $1.45 | $1.45 | $1.21 | $1.21 |
| 10 | 0805 0.1uF ceramic | capacitor | Digi-Key | N/A | $0.00 | $0.03 | $0.30 |
| 4 | 0805 1.0uF ceramic | capacitor | Digi-Key | N/A | $0.00 | $0.06 | $0.24 |
| 2 | 0805 2.2uF ceramic | capacitor | Digi-Key | N/A | $0.00 | $0.08 | $0.16 |
| 2 | 0805 47uF tantalum | capacitor | Digi-Key | N/A | $0.00 | $0.71 | $1.42 |
| 2 | 0805 4.7K ohm | resistor | Digi-Key | N/A | $0.00 | $0.01 | $0.02 |
| 1 | 0805 390 ohm | resistor | Digi-Key | N/A | $0.00 | $0.01 | $0.01 |
| $37.20 | $32.01 |
5 Comments so far
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Count me in if you are wondering if anyone is interested in buying one of these units. It would also be nice to see your (menu) code as well.
Have you considered using accelerometers (e.g. two, for 2-axis analysis) to count steps? Texas Instruments should have some in their sample program so you could give it a try.
In single-unit quantities the voltage regulator and EEPROM and both more expensive than the microcontroller itself. That’s a bit annoying… time to rethink the design.
I did look into using an accelerometer a bit, but I think it would be more expensive and more power usage than just a simple vibration switch. Of course it would also be more accurate!
For the step-up converter have a look at the TI TPS61221. It has a fixed output of 3.3V and needs only 3 additional parts. It’s 2.63 USD in single quantities and only 1.84 USD for 100 (Digi-Key 296-24171-1-ND).
The EEPROM can be replaced with the M95M01-RMW6G. It’s 3.44 USD for 1 (Digi-Key 497-8617-5-ND). This chip has an serial interface and therefore needs one additional pin from your uC.
The 24AA1025T-I/SN would be an I2C alternative (Digi-Key 24AA1025T-I/SNCT-ND).
TI has a great sample program so you could try out the TPS61221 for next to nothing.
Keep on the good work!
Hello, I am looking for a datalogger to measure 4-20ma or 0-10 vdc.
it would be easier if I could talk to you and tell you my requirements so if you would like to phone me or email me and we can talk.
many thanks
alan thompson