luchiand
Posts: 29
Joined: Sun Feb 24, 2019 8:36 am

Can I use 5V to power a display with tm1637 and control it by 3 V

Thu May 16, 2019 7:44 am

I have a tm163 based display. Unfortunately the provider did not specify anything about the color. I did not care about the color when I bought it. The provider has not another one, so that there is no way to find if this information would have been available.

I am afraid if it is blue, the 3 V is not enough. But can I control it by 3 V? There are 4 pins, 2 for power, Data In (DIN) and Clock (CLK) . So can I use DIN and CLK on 3 V pins if it is powered on 5V?

I did not found any way to make it work. The documentation is poor and mostly for
clock-like display. Mine is the type with decimal dots.
Any help will be appreciated.

pcmanbob
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Re: Can I use 5V to power a display with tm1637 and control it by 3 V

Thu May 16, 2019 9:30 am

I would say that very much depends on the specifications of the TM163 based display in question, if the TM163 will recognise 3.3v as being a high input with reference to the 5V supply then yes it may be possible.

But you would need to check the specifications to see what is specified as the high input voltage minimum with reference to the supply voltage, to be sure it would work.
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luchiand
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Joined: Sun Feb 24, 2019 8:36 am

Re: Can I use 5V to power a display with tm1637 and control it by 3 V

Thu May 16, 2019 3:28 pm

I know that it can use also 3 or 5 V. I don’t know what color it ia. Blue would be very dim with 3 V..

pcmanbob
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Re: Can I use 5V to power a display with tm1637 and control it by 3 V

Thu May 16, 2019 8:35 pm

luchiand wrote:
Thu May 16, 2019 3:28 pm
I know that it can use also 3 or 5 V. I don’t know what color it ia. Blue would be very dim with 3 V..
I answered the question you asked " Can I use 5V to power a display with tm1637 and control it by 3 V " but it could only be a generalisation because I don't know which display you are using as you have not provided that information,
and I have no idea what colour it will be either, the only person who can answer that and provide a definitive answer to your question is the person who supplied it, so I suggest you contact them.
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mahjongg
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Re: Can I use 5V to power a display with tm1637 and control it by 3 V

Fri May 17, 2019 12:26 pm

You need to find the datasheet for the TM1637 chip, and look up the minimum Logic High Level (ViH), if its something like 2.0V, then 3.3V will work, but if it is something like 70% of Vcc, then that is 3.5V when powered with 5V, and that is too much, and won't work reliably. Solution, either a level converter to crank up the logic levels above 3.5V, or lower Vcc somewhat so 70% of it is below 3.3V.

Anthony S
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Re: Can I use 5V to power a display with tm1637 and control it by 3 V

Fri May 17, 2019 3:05 pm

Hi luchiand,

According to the TM1637 datasheet, the minimum high-level input voltage is specified as 0.7*VDD, i.e., 70% of the supply voltage. So with VDD = 5V, the device would recognise a minimum voltage level of 3.5V as a logic high - some 0.2V higher than the Pi's 3.3V logic high level, so it's highly unlikley that you would get reliable operation, if any at all.

The TM1637 is specified for operation over the VDD range 4.5 - 5.5V, so if you ran your display at 4.5V, the corresponding minimum logic high level would be 0.7*4.5 = 3.15V. This is only 0.15V below the Pi's 3.3V high level, so even though it would probably work, it would provide very poor noise margins and could lead to problems with supply tolerances.

A much better solution would be to run your display at 5V and provide your logic levels via an interface device which would provide voltage level translation and guarantee reliable operation. For example, a hex Schmitt trigger such as the 74HCT14 has a maximum positive-going threshold voltage of around 2.0V when operating from a 5V supply. Remember:

1. The device has to be a 74HCT14, not a 74HC14;
2. The 74HCT14 has to be powered from the 5V supply, not 3.3V;
3. Each of the gates is an inverting device, so you need two in series to maintain the correct logic level.

Good luck,

Tony.

luchiand
Posts: 29
Joined: Sun Feb 24, 2019 8:36 am

Re: Can I use 5V to power a display with tm1637 and control it by 3 V

Sun May 19, 2019 8:01 am

It was my library on raspberry faulty. I put it on an Arduino first to make sure ir works. Then I found a better library and works on Raspberry, too. The only problem now is that I can not control the decimal dots. But I can put off that for a while.

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