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8 bit PIC with RTC chip.

asanyi

Hi, my circuit is composed from a PIC16F15345 microcontroller and a MCP79411 RTC chip, connected with i2c, it has an own 32.768 crystal. The 16F15345 also drives deprez meters and LEDs with PWM signals. While the power of the main circuit is switched off, the RTC runs correctly (precise timing) from its backup 3V battery. But activating the power of the PIC and the PWM driving, the RTC has lost its correct operation, delaying 30 minutes per 12 hour! Any idea to fix is accepted...

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  • You need to show us the circuit diagram and ideally some pictures of the hardware.

    The kind of problem you describe is often caused by bad layout, inadequate power supply decoupling or ciruit errors.

    Without more information it is not possible to tell which, if any, is the cause here.

    MK

  • in reply to michaelkellett

    Michael, thanks for the fast response. Well, the project was quite simple with fast building, so there is only a handmade schematic and the circuit is soldered to a prototype PCB. But I try by words... Power supply, step by step the components: and old NOKIA cell phone charger with 6...8V DC output, 1000uF/16V electrolit + 100nF ceramic capacitor, L4941 low drop 5V regulator, 1uF tantalium capacitor on output. PIC: 100nF ceramic closest to its pin1/pin20 power connections. PIC works with internal osc, 32MHz. RTC: 100nF ceramic closest to its pin4/pin8 connections. RTC osc: 32.768 crystal on pin1 and pin2 (closest), 2x22pF ceramic. Remark: the MCP79411 datasheet offers 6pF capacitors, but trying these, not working. The rest of the circuit (2 LEDs and 2 deprez solenoids from 4 PWM output) has all together 15mA current consumption with 100 duty. Thats all. Maybe the problem is caused around the RTC crystal/capacitor fail fitting. But it is clear, only at activated PWM signals detected. Anyway, similar issue was detected at my earlier project, a vintage Nixie-tube clock. When I tried to regulate the light of the nixies by switching PWM the 170V DC nixie power, the RTC went to fail timing. With different PIC, but with the same RTC.

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  • in reply to michaelkellett

    Michael, thanks for the fast response. Well, the project was quite simple with fast building, so there is only a handmade schematic and the circuit is soldered to a prototype PCB. But I try by words... Power supply, step by step the components: and old NOKIA cell phone charger with 6...8V DC output, 1000uF/16V electrolit + 100nF ceramic capacitor, L4941 low drop 5V regulator, 1uF tantalium capacitor on output. PIC: 100nF ceramic closest to its pin1/pin20 power connections. PIC works with internal osc, 32MHz. RTC: 100nF ceramic closest to its pin4/pin8 connections. RTC osc: 32.768 crystal on pin1 and pin2 (closest), 2x22pF ceramic. Remark: the MCP79411 datasheet offers 6pF capacitors, but trying these, not working. The rest of the circuit (2 LEDs and 2 deprez solenoids from 4 PWM output) has all together 15mA current consumption with 100 duty. Thats all. Maybe the problem is caused around the RTC crystal/capacitor fail fitting. But it is clear, only at activated PWM signals detected. Anyway, similar issue was detected at my earlier project, a vintage Nixie-tube clock. When I tried to regulate the light of the nixies by switching PWM the 170V DC nixie power, the RTC went to fail timing. With different PIC, but with the same RTC.

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