About the article

Precision Barometer/Altimeter

with temperature readout

Precision Barometer/Altimeter
Based on the MS5534 pressure sensor made by the Swiss company INTERSEMA (specialized in pressure measurements), with one metre resolution in altitude, this circuit will also give you absolute pressure, temperature, and even the time of day. The microcontroller used in the instrument is the now well established PIC16F876.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Extra info, Update
New software that solves the problems with the real-time clock is now available from our website (ref. 040313-11.zip).

Problems with the real-time clock may be solved by downloading updated software from our website. A 56-pF capacitor between pin 12 of IC1 and ground will improve the clock accuracy.

Due to a change in the control software, a few small modifications are required on PCB no. 040313-1. The modified PCB design can be downloaded here (ref. 040313-PCB.pdf). PCBs already supplied through Readers Services, or made at home using the artwork originally supplied, may be modified as detailed below.
The two PCB tracks leading to pin 1 (MCLR) of IC2 are cut as close as possible to the IC pin and then connected to each another only, using a small piece of wire. The track between pin 4 (RA2) of IC2 and junction R7/S1 is cut in the vicinity of pin 4. Next, the interrupted track coming from R7/S1 is connected to pin 1 of IC2.
R1 = 2k2
R2 = 33
R3 = 330k
R4 = 180k
R5,R6,R7 = 4k7
R8 = 1k
R9 = 1k5
P1 = 10k
C1, C2 = 22pF
C3,C4 = 100nF
D1 = 1N4001
D2,D3 = 1N4148
IC1 = ICL7663
IC2 = PIC16F876, programmed, order code 040313-41)
IC3 = MS5534 (Intersema)
K1 = 9-way sub-D socket (female), PCB mount, angled pins
K2 = HE-10 connector, 2 rows of 8 contacts
S1,S2,S3 = pushbutton DTS63N
X1 = 8MHz quartz crystal, miniature case
X2 = 32.768kHz quartz crystal
LCD, 2x206 characters, e.g., Vikay 2220
28-way IC socket
PCB, ref, 040313-1 from The PCBShop
Project software, code 040313-11
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