Click Here for the HLA
44k' source code
Click Here for the HLA
100k' source code
Click Here for the HLA High Altitude Sensor source code in meters
Click Here for the PCB123 file. You can download the free PCB123 design software from Sunstone Circuits. You can also order boards directly from the design software. Note: This version of the PCB has the traces for the jumper shunts included, you won't need to add the wire on the bottom of the board as shown later.
The below 3 tables show vacuum chamber test results. I used a Missile Works RRC2x altimeter to compare the results
from the HLA2 altimeter. Keep in mind the degree of error on the sensors is 2-2.5%, so it is possible for the altimeters
to be within spec and still be as much as 5% off.
| HLA (high) Reported Altitude | RRCX2 Reported Altitude | HLA/RRCX2 Variance |
| 910 | 830 | +80 |
| 910 | 830 | +80 |
| 5,330 | 5,200 | +130 |
| 6,040 | 5,900 | +140 |
| 6,580 | 6,482 | +98 |
| 6,860 | 6,892 | -32 |
| 7,080 | 7,044 | +36 |
| 7,900 | 8,108 | -208 |
| 8,520 | 8,564 | -44 |
| 8,700 | 8,752 | -52 |
| 8,860 | 8,716 | +144 |
| 12,060 | 11,908 | +152 |
| 12,090 | 12,078 | +12 |
| 13,510 | 13,555 | -45 |
| 14,250 | 14,104 | +146 |
| 14,380 | 14,287 | +93 |
| 15,000 | 14,848 | +152 |
| 15,200 | 15,043 | +147 |
| 16,230 | 16,331 | -101 |
| 16,870 | 16,930 | -60 |
| 18,100 | 18,275 | -175 |
| 20,470 | 20,547 | -77 |
| 20,890 | 20,764 | +126 |
| 22,430 | 22,437 | -7 |
| 22,530 | 22,676 | -146 |
| 22,710 | 22,676 | +34 |
| 23,090 | 23,320 | -230 |
| 27,270 | 27,408 | -138 |
| 30,330 | 30,576 | -280 |
| 36,010 | 35,999 | +11 |
| 42,840 | 42,657 | RRC2X over limit |
| 48,080 | 42,657 | RRC2X over limit |
| 48,550 | - | RRC2X over limit |
| HLA (low) Reported Altitude | RRC2x Reported Altitude | HLA/RRCX2 Variance |
| 3,970 | 4,008 | -38 |
| 5,570 | 5,524 | +46 |
| 7,690 | 7,720 | -30 |
| 9,830 | 9,866 | -36 |
| 11,000 | 10,992 | +8 |
| 14,860 | 14,925 | -65 |
| 16,030 | 16,018 | +12 |
| 18,930 | 19,127 | -197 |
| 21,570 | 21,245 | +325 |
| 23,770 | 23,964 | -194 |
| 24,740 | 24,472 | +268 |
| 27,190 | 27,115 | +75 |
| 27,770 | 27,583 | +187 |
| 35,470 | 35,763 | -293 |
| HLA 100k' | HLA44k' | RRC2x |
| 4,170 | 4,090 | 4,154 |
| 5,380 | 5,270 | 5,266 |
| 10,380 | 10,290 | 10,364 |
| 15,800 | 15,880 | 15,782 |
| 16,140 | 16,160 | Battery lost contact |
| Battery lost contact | 21,510 | 21,605 |
| 29,860 | 30,150 | 30,222 |
Notice twice I had batteries that lost contact during the test. I was using some pretty old snap on connectors. But this is another example of why not to use clip on 9 volt battery connectors. I solder my power wires directly to the batteries.
Parts Placement guide.
Here's another image showing the bare board next to a completed board.
Bottom side of board showing jumper wire installed between 2 position header pins and +5 volts. This jumper wire is required because of an error of omission on my part when designing the board. Make sure the jumper wire is installed exactly as shown and does not touch any other solder pads. The new version of the board in PCB123 has the proper traces included, so if you order your own boards you won't need to include this jumper wire.
Parts List:
9) 10k Ohm 1/8 watt resistors DigiKey part
2) 1k Ohm 1/8 watt resistors DigiKey part
1) 10 uF electrolytic capacitor DigiKey part
1) 28 pin socket DigiKey part
1) 40 pin Breakaway header DigiKey part
3) terminal blocks DigiKey part
2) IRF 510 transistors DigiKey part
1) piezo buzzer DigiKey part
1) LM7805CT voltage regulator DigiKey part
1) .22 uF capacitor (If using 100k' sensor) DigiKey part
4) Shunts DigiKey part
1) either MPX5100a sensor (44,000' version) DigiKey part
or 1) Honeywell ASDX015A24R sensor (100,000' version) DigiKey part
1) Basic Micro Nano 28 Basic Micro Part
To program the altimeter you will need the Basic Micro IDE software as well as a programmer. Lastly you will need a 3 wire cable to go between the
programmer and the altimeter board. I've been using a four pin header for programming, even though only 3 pins
are used. The four pin header connector is part number a26983-nd and the internal sockets are part number a25955-nd. If you're only making up an altimeter or two, the connector
and socket aren't absolutely needed, you could simply solder wires or even use alligator clips. Refer to the Basic Micro documentation and the
users manual on how to wire the programmer.