# 6.5 Digit voltage display

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#### shekhar87

##### Newbie level 6 Hi guys,
I am looking for 6.5 digit LED voltage display circuit with a 10mV resolution. I do not know how to design this circuit. What methodology i can use to display voltage on seven segment LED?
Please give me some input ASAP?
P.S: Any one has reference schematic circuit?

#### alexan_e You can use an MCU to show the result

What is the range that you want, you said 10mV but for what voltage?
An MCU can give a 5mV resolution for 5v using a 10bit ADC, you will probably have to use an external ADC of 13-14 bit

Alex

#### shekhar87

##### Newbie level 6 Hi Alexan-e
i am designing power supply and the range of voltage is 0-1000 V with 10 mV resolution.
I need to display the voltage for the same.

#### alexan_e 1000v with 10mv resolution is 1/100000 so you need 17bit ADC that can give a resolution of 1/131071 but then your problem will be to use a divider to lower this voltage to a level that the ADC can work with (depends on the ADC ref voltage) and still be able to keep the noise in very low level to have a correct measurement, I have no idea how to do that.

Assume that you have 1000v input, to fir that in a 5v ADC you need to divide it with 200.
Now imagine that you have 0.1v and you divide it also with 200, the result will be 0.5mv so you can easily have noise problems.
Maybe you can do it with variable dividers depending on the range, I can't give you any recommendation because the voltage is too high and I have never done anything similar

Alex

#### shekhar87

##### Newbie level 6 1000v with 10mv resolution is 1/100000 so you need 17bit ADC that can give a resolution of 1/131071 but then your problem will be to use a divider to lower this voltage to a level that the ADC can work with (depends on the ADC ref voltage) and still be able to keep the noise in very low level to have a correct measurement, I have no idea how to do that.

Assume that you have 1000v input, to fir that in a 5v ADC you need to divide it with 200.
Now imagine that you have 0.1v and you divide it also with 200, the result will be 0.5mv so you can easily have noise problems.
Maybe you can do it with variable dividers depending on the range, I can't give you any recommendation because the voltage is too high and I have never done anything similar

Alex
how did you calculate that i require 17 bit ADC?
And what is 1/131071?

#### alexan_e A 4 bit ADC can give a result of 0000 to 1111, to calculate the range of values that this 4bit can give you can do (2^4)-1=15 [^ is the raise to power symbol]
for a 16bit ADC you can have 0000000000000000 to 1111111111111111 and the possible values are (2^16)-1=65535
The 17bit ADC can double that resolution and give up to 131071 , by 1/131071 ! mean that you can get the result with a resolution of 1 part in 131071 (1/131071) of the ADC reference.
when you want to have a 10mV resolution for 1000v you are asking for 1/100000 so the ADC should be able to provide at least 100000 different values, a 16bit can't do that , you have to go to at least a 17bit ADC

Alex

#### shekhar87

##### Newbie level 6 A 4 bit ADC can give a result of 0000 to 1111, to calculate the range of values that this 4bit can give you can do (2^4)-1=15 [^ is the raise to power symbol]
for a 16bit ADC you can have 0000000000000000 to 1111111111111111 and the possible values are (2^16)-1=65535
The 17bit ADC can double that resolution and give up to 131071 , by 1/131071 ! mean that you can get the result with a resolution of 1 part in 131071 (1/131071) of the ADC reference.
when you want to have a 10mV resolution for 1000v you are asking for 1/100000 so the ADC should be able to provide at least 100000 different values, a 16bit can't do that , you have to go to at least a 17bit ADC

Alex
thank you so much for this explanation

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