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Topic: MAX7219 + Relay Shield (Read 295 times) previous topic - next topic

EXIA_00

Hello Eveyone and Good Day!, This semester I am taking my thesis and I would like to ask if it is possible to control a relay using a MAX7219

PaulRB

Hi,

No. Max7219 is designed to drive LEDs, not relays. It uses multiplexing to fool the eye that up to 64 leds are on, when in fact only up to 8 are on at any instant. The eye is fooled because of an effect known as Persistence of Vision.

Persistence of Vision would not work on relays! They would probably not work at all, because of the speed of the multiplexing performed by the chip, plus the higher current requirements of relay coils compared to leds. Even if the relays could operate fast enough and needed only small currents, they would wear out mechanically in no time because they would be rapidly switching on and off.

If you need to operate a large number of relays, look at TPIPC6A/B/C595 chips. Each chip can drive 8 relays and the chips can be daisy-chained so that only 3 Arduino pins are used.

EXIA_00

I see thank you very much for answering my question. Can I ask for the link of the IC chip that you were talking about?
 

PaulRB

#3
Dec 01, 2017, 05:24 pm Last Edit: Dec 01, 2017, 05:26 pm by PaulRB
There are several versions of the chip. They are all very similar except that their outputs are rated for different currents. You can choose the cheapest available of the models that can handle the current your relays need.

TPIC6595
TIPC6A595
TPIC6B595
TPIC6C595
TPIC6D595

However, if you are planning to use relay modules which have built-in driver transistors, you can use the much cheaper and commonly available 74HC595 or 74LS595.

EXIA_00

Thank you I will make it a reference and study how to use this in relay

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