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GCA119 Time / temperature display unit for buildings


By Peter Giling


A further completion of your railroad set-up is to have a time/temperature display.

This type of unit is seen at various places near bank-buidings etc.

MGV119 is the processor that will control four 7-segment displays.

These displays have a wide variety of sizes.

One example is GCA118.

MGV119 is provided with two special chips for time (PCF8583) and temperature (DS1621).

A PIC16F873 processor will read both chips by use of I2C connection.

A Gold cap capacitor will provide that clock chip keeps running for several days without power.

The unit is supplied by anything between 8 and 18V ac/dc.

The total power consumpion at 12 Vdc is approx 0,3Watt.

To make the display itself as small as possible, the connecting wires to J1 and J2 from display to GCA119 are directly soldered to the back plane of diplays.

The picture of the prototype will show how it's made.

Three buttons (only two on prototype) provide the way of setting hours and minutes.

Switching between time and temperature is done with an interval of 3 seconds.

To reduce power consumption, the processor will active only one display at the same time, and ach display will light up for 5 milliseconds, in a constant sequence.

The minutes are changed by pressing S1 for increasing and pressing s2 for decreasing.

Holding s3 pressed down, the buttons s1 and s2 will change hour.

Time is automaticly saved in chip PCF8583 after changing.

With little efford, it would be possible to display DATE as well. The clock chip is ready for it.

If that is a desirable option, I will add it too.

The displays, as used here, are not weel suited for this. Actually, the time also needs ":" instead of "." as is now between hours and mintes.

To be able to see if time or date is displayed, I think these readmarks are indispensable.

The prototype picture

This shows MGV118 and MGV119 together
showing time
pretty warm up here

The firmware

Bill of materials

Amount Reference Description
5 R1,R2,R4,R5,R11 3K3
1 R3 100E
4 R6,R7,R8,R9 4K7
1 R10 10K
1 RP1 ARRAY 8 x 150 Ohm
1 C1 15pF
1 C2 ELCO 0,25 F Goldcap 5,5V
1 C3 ELCO 470uF 25V
1 C4 ELCO 10 uF
2 C5,C6 100 nF
2 C7,C8 15 pF
4 T1,T2,T3,T4 BC547b
1 U1 PIC16F873
1 U2 PCF8583
1 U3 DS1621
1 VR1 7805
1 GR1 B80C1500 Round
1 F1 Multifuse 0,3A
1 J1 PSS 254/10G
1 J2 PSS 254/5G
1 J3 akl012-02
2 S1,S2 pushbutton
1 X1 CRYSTAL 32765 Hz 156098 CONRAD

The design

The files for D.I.Y. pcb
The schematics
The pcb + parts placement
N.B. Self made pc-boards are not supported!
mgv119-en.txt · Last modified: 2018/11/12 08:56 (external edit)