Seven-segment display seems to draw little current
Clash Royale CLAN TAG#URR8PPP
up vote
17
down vote
favorite
I bought a 1.8-inch seven-segment common cathode LED display from AliExpress. So no datasheet available.
I used a 1 kΩ resistor and a 5 V source, as to put a max 5 mA in the LED. I measured 1.6 V for the decimal dot, and 3.5 V for each segment. The measured current draw for one segment was 1.5 mA.
Now, I expected each LED to be quite dim at 1.5 mA, but it was the opposite, I could put a 4 kΩ resistor and still has a usable display.
I intended to drive the display using an ATmega328P and a MAX7219 (which would have been OK up to 500Â mA per segment).
Does this measurement seem correct, and if so, I can drop the MAX7219 and drive the segment directly (with current limiting resistors) with the ATmega?
current-measurement 7segmentdisplay atmega328p
edited Aug 24 at 0:56
Peter Mortensen
1,56131422
asked Aug 21 at 11:19
mathieu
1888
add a comment |Â
up vote
17
down vote
favorite
I bought a 1.8-inch seven-segment common cathode LED display from AliExpress. So no datasheet available.
I used a 1 kΩ resistor and a 5 V source, as to put a max 5 mA in the LED. I measured 1.6 V for the decimal dot, and 3.5 V for each segment. The measured current draw for one segment was 1.5 mA.
Now, I expected each LED to be quite dim at 1.5 mA, but it was the opposite, I could put a 4 kΩ resistor and still has a usable display.
I intended to drive the display using an ATmega328P and a MAX7219 (which would have been OK up to 500Â mA per segment).
Does this measurement seem correct, and if so, I can drop the MAX7219 and drive the segment directly (with current limiting resistors) with the ATmega?
current-measurement 7segmentdisplay atmega328p
edited Aug 24 at 0:56
Peter Mortensen
1,56131422
asked Aug 21 at 11:19
mathieu
1888
A modern single digit is easy to drive directly from a micro. If you need to drive multiple digits it gets more difficult. The digit drivers will be that DC segment current * n * 8 for n digits.
– Spehro Pefhany
Aug 21 at 12:09
@SpehroPefhany I need to drive 2 digits, but I have plenty of spare IO on my atmega328p ;) I could use this as an opportunity to multiplex.
– mathieu
Aug 21 at 12:13
I've found that modern LEDs are a lot brighter than I think. I use 10k at 5V when breadboarding stuff and it's still plenty bright as an indicator (indoors, anyway). Except for yellow ones for some reason.
– immibis
Aug 22 at 2:40
Note that max current draw for Microcontrollers typically is two specs: per pin and total current limit. And, typically,total != npins*max_per_pin
– crasic
Aug 22 at 6:12
add a comment |Â
up vote
17
down vote
favorite
up vote
17
down vote
favorite
I bought a 1.8-inch seven-segment common cathode LED display from AliExpress. So no datasheet available.
I used a 1 kΩ resistor and a 5 V source, as to put a max 5 mA in the LED. I measured 1.6 V for the decimal dot, and 3.5 V for each segment. The measured current draw for one segment was 1.5 mA.
Now, I expected each LED to be quite dim at 1.5 mA, but it was the opposite, I could put a 4 kΩ resistor and still has a usable display.
I intended to drive the display using an ATmega328P and a MAX7219 (which would have been OK up to 500Â mA per segment).
Does this measurement seem correct, and if so, I can drop the MAX7219 and drive the segment directly (with current limiting resistors) with the ATmega?
current-measurement 7segmentdisplay atmega328p
edited Aug 24 at 0:56
Peter Mortensen
1,56131422
asked Aug 21 at 11:19
mathieu
1888
I bought a 1.8-inch seven-segment common cathode LED display from AliExpress. So no datasheet available.
I used a 1 kΩ resistor and a 5 V source, as to put a max 5 mA in the LED. I measured 1.6 V for the decimal dot, and 3.5 V for each segment. The measured current draw for one segment was 1.5 mA.
Now, I expected each LED to be quite dim at 1.5 mA, but it was the opposite, I could put a 4 kΩ resistor and still has a usable display.
I intended to drive the display using an ATmega328P and a MAX7219 (which would have been OK up to 500Â mA per segment).
Does this measurement seem correct, and if so, I can drop the MAX7219 and drive the segment directly (with current limiting resistors) with the ATmega?
current-measurement 7segmentdisplay atmega328p
current-measurement 7segmentdisplay atmega328p
edited Aug 24 at 0:56
Peter Mortensen
1,56131422
asked Aug 21 at 11:19
mathieu
1888
edited Aug 24 at 0:56
Peter Mortensen
1,56131422
asked Aug 21 at 11:19
mathieu
1888
edited Aug 24 at 0:56
Peter Mortensen
1,56131422
edited Aug 24 at 0:56
Peter Mortensen
1,56131422
edited Aug 24 at 0:56
Peter Mortensen
1,56131422
1,56131422
asked Aug 21 at 11:19
mathieu
1888
asked Aug 21 at 11:19
mathieu
1888
asked Aug 21 at 11:19
mathieu
1888
1888
A modern single digit is easy to drive directly from a micro. If you need to drive multiple digits it gets more difficult. The digit drivers will be that DC segment current * n * 8 for n digits.
– Spehro Pefhany
Aug 21 at 12:09
@SpehroPefhany I need to drive 2 digits, but I have plenty of spare IO on my atmega328p ;) I could use this as an opportunity to multiplex.
– mathieu
Aug 21 at 12:13
I've found that modern LEDs are a lot brighter than I think. I use 10k at 5V when breadboarding stuff and it's still plenty bright as an indicator (indoors, anyway). Except for yellow ones for some reason.
– immibis
Aug 22 at 2:40
Note that max current draw for Microcontrollers typically is two specs: per pin and total current limit. And, typically,total != npins*max_per_pin
– crasic
Aug 22 at 6:12
add a comment |Â
A modern single digit is easy to drive directly from a micro. If you need to drive multiple digits it gets more difficult. The digit drivers will be that DC segment current * n * 8 for n digits.
– Spehro Pefhany
Aug 21 at 12:09
@SpehroPefhany I need to drive 2 digits, but I have plenty of spare IO on my atmega328p ;) I could use this as an opportunity to multiplex.
– mathieu
Aug 21 at 12:13
I've found that modern LEDs are a lot brighter than I think. I use 10k at 5V when breadboarding stuff and it's still plenty bright as an indicator (indoors, anyway). Except for yellow ones for some reason.
– immibis
Aug 22 at 2:40
Note that max current draw for Microcontrollers typically is two specs: per pin and total current limit. And, typically,total != npins*max_per_pin
– crasic
Aug 22 at 6:12
A modern single digit is easy to drive directly from a micro. If you need to drive multiple digits it gets more difficult. The digit drivers will be that DC segment current * n * 8 for n digits.
– Spehro Pefhany
Aug 21 at 12:09
A modern single digit is easy to drive directly from a micro. If you need to drive multiple digits it gets more difficult. The digit drivers will be that DC segment current * n * 8 for n digits.
– Spehro Pefhany
Aug 21 at 12:09
@SpehroPefhany I need to drive 2 digits, but I have plenty of spare IO on my atmega328p ;) I could use this as an opportunity to multiplex.
– mathieu
Aug 21 at 12:13
@SpehroPefhany I need to drive 2 digits, but I have plenty of spare IO on my atmega328p ;) I could use this as an opportunity to multiplex.
– mathieu
Aug 21 at 12:13
I've found that modern LEDs are a lot brighter than I think. I use 10k at 5V when breadboarding stuff and it's still plenty bright as an indicator (indoors, anyway). Except for yellow ones for some reason.
– immibis
Aug 22 at 2:40
I've found that modern LEDs are a lot brighter than I think. I use 10k at 5V when breadboarding stuff and it's still plenty bright as an indicator (indoors, anyway). Except for yellow ones for some reason.
– immibis
Aug 22 at 2:40
Note that max current draw for Microcontrollers typically is two specs: per pin and total current limit. And, typically,
total != npins*max_per_pin– crasic
Aug 22 at 6:12
Note that max current draw for Microcontrollers typically is two specs: per pin and total current limit. And, typically,
total != npins*max_per_pin– crasic
Aug 22 at 6:12
add a comment |Â
2 Answers
2
active
oldest
votes
up vote
19
down vote
accepted
First of all +1 for measuring your display. Too often we get questions here about "I saved money by buying cheap from Alibaba but it don't work. Now please spend you valuable time helping me out".
These days LED's are very efficient. They no longer need the 20mA the first generation required. 1mA or less is not uncommon.
So, yes, you drive these straight from an atmega328.
answered Aug 21 at 11:28
Oldfart
7,0732723
3
Thanks. A lot of the fun is learning of this works, and comparing expected vs real values with the multimeter. Now, I have some ripup to do in Eagle ;)
– mathieu
Aug 21 at 11:44
9
It also depends on the surrounding lighting, in daylight you are going to need to drive them harder to literally outperform the sun, in the dark you only need enough to be glowing at all.
– ratchet freak
Aug 21 at 12:48
add a comment |Â
up vote
0
down vote
Use current limit resistors. You can get by with 1 if you are multplexing the display (only turning on 1 segment at a time), or use 7 if you are driving all 7 at once. The advantage of the MAX7219 is that takes cares of the multiplexing for you, and can drive up to 8 digits with just 3 outputs from the Atmega328P.
answered Aug 21 at 16:55
CrossRoads
6024
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
19
down vote
accepted
First of all +1 for measuring your display. Too often we get questions here about "I saved money by buying cheap from Alibaba but it don't work. Now please spend you valuable time helping me out".
These days LED's are very efficient. They no longer need the 20mA the first generation required. 1mA or less is not uncommon.
So, yes, you drive these straight from an atmega328.
answered Aug 21 at 11:28
Oldfart
7,0732723
3
Thanks. A lot of the fun is learning of this works, and comparing expected vs real values with the multimeter. Now, I have some ripup to do in Eagle ;)
– mathieu
Aug 21 at 11:44
9
It also depends on the surrounding lighting, in daylight you are going to need to drive them harder to literally outperform the sun, in the dark you only need enough to be glowing at all.
– ratchet freak
Aug 21 at 12:48
add a comment |Â
up vote
19
down vote
accepted
First of all +1 for measuring your display. Too often we get questions here about "I saved money by buying cheap from Alibaba but it don't work. Now please spend you valuable time helping me out".
These days LED's are very efficient. They no longer need the 20mA the first generation required. 1mA or less is not uncommon.
So, yes, you drive these straight from an atmega328.
answered Aug 21 at 11:28
Oldfart
7,0732723
3
Thanks. A lot of the fun is learning of this works, and comparing expected vs real values with the multimeter. Now, I have some ripup to do in Eagle ;)
– mathieu
Aug 21 at 11:44
9
It also depends on the surrounding lighting, in daylight you are going to need to drive them harder to literally outperform the sun, in the dark you only need enough to be glowing at all.
– ratchet freak
Aug 21 at 12:48
add a comment |Â
up vote
19
down vote
accepted
up vote
19
down vote
accepted
First of all +1 for measuring your display. Too often we get questions here about "I saved money by buying cheap from Alibaba but it don't work. Now please spend you valuable time helping me out".
These days LED's are very efficient. They no longer need the 20mA the first generation required. 1mA or less is not uncommon.
So, yes, you drive these straight from an atmega328.
answered Aug 21 at 11:28
Oldfart
7,0732723
First of all +1 for measuring your display. Too often we get questions here about "I saved money by buying cheap from Alibaba but it don't work. Now please spend you valuable time helping me out".
These days LED's are very efficient. They no longer need the 20mA the first generation required. 1mA or less is not uncommon.
So, yes, you drive these straight from an atmega328.
answered Aug 21 at 11:28
Oldfart
7,0732723
answered Aug 21 at 11:28
Oldfart
7,0732723
answered Aug 21 at 11:28
Oldfart
7,0732723
answered Aug 21 at 11:28
Oldfart
7,0732723
7,0732723
3
Thanks. A lot of the fun is learning of this works, and comparing expected vs real values with the multimeter. Now, I have some ripup to do in Eagle ;)
– mathieu
Aug 21 at 11:44
9
It also depends on the surrounding lighting, in daylight you are going to need to drive them harder to literally outperform the sun, in the dark you only need enough to be glowing at all.
– ratchet freak
Aug 21 at 12:48
add a comment |Â
3
Thanks. A lot of the fun is learning of this works, and comparing expected vs real values with the multimeter. Now, I have some ripup to do in Eagle ;)
– mathieu
Aug 21 at 11:44
9
It also depends on the surrounding lighting, in daylight you are going to need to drive them harder to literally outperform the sun, in the dark you only need enough to be glowing at all.
– ratchet freak
Aug 21 at 12:48
3
3
Thanks. A lot of the fun is learning of this works, and comparing expected vs real values with the multimeter. Now, I have some ripup to do in Eagle ;)
– mathieu
Aug 21 at 11:44
Thanks. A lot of the fun is learning of this works, and comparing expected vs real values with the multimeter. Now, I have some ripup to do in Eagle ;)
– mathieu
Aug 21 at 11:44
9
9
It also depends on the surrounding lighting, in daylight you are going to need to drive them harder to literally outperform the sun, in the dark you only need enough to be glowing at all.
– ratchet freak
Aug 21 at 12:48
It also depends on the surrounding lighting, in daylight you are going to need to drive them harder to literally outperform the sun, in the dark you only need enough to be glowing at all.
– ratchet freak
Aug 21 at 12:48
add a comment |Â
up vote
0
down vote
Use current limit resistors. You can get by with 1 if you are multplexing the display (only turning on 1 segment at a time), or use 7 if you are driving all 7 at once. The advantage of the MAX7219 is that takes cares of the multiplexing for you, and can drive up to 8 digits with just 3 outputs from the Atmega328P.
answered Aug 21 at 16:55
CrossRoads
6024
add a comment |Â
up vote
0
down vote
Use current limit resistors. You can get by with 1 if you are multplexing the display (only turning on 1 segment at a time), or use 7 if you are driving all 7 at once. The advantage of the MAX7219 is that takes cares of the multiplexing for you, and can drive up to 8 digits with just 3 outputs from the Atmega328P.
answered Aug 21 at 16:55
CrossRoads
6024
add a comment |Â
up vote
0
down vote
up vote
0
down vote
Use current limit resistors. You can get by with 1 if you are multplexing the display (only turning on 1 segment at a time), or use 7 if you are driving all 7 at once. The advantage of the MAX7219 is that takes cares of the multiplexing for you, and can drive up to 8 digits with just 3 outputs from the Atmega328P.
answered Aug 21 at 16:55
CrossRoads
6024
Use current limit resistors. You can get by with 1 if you are multplexing the display (only turning on 1 segment at a time), or use 7 if you are driving all 7 at once. The advantage of the MAX7219 is that takes cares of the multiplexing for you, and can drive up to 8 digits with just 3 outputs from the Atmega328P.
answered Aug 21 at 16:55
CrossRoads
6024
answered Aug 21 at 16:55
CrossRoads
6024
answered Aug 21 at 16:55
CrossRoads
6024
answered Aug 21 at 16:55
CrossRoads
6024
6024
add a comment |Â
add a comment |Â
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2felectronics.stackexchange.com%2fquestions%2f392036%2fseven-segment-display-seems-to-draw-little-current%23new-answer', 'question_page');
);
Post as a guest
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
A modern single digit is easy to drive directly from a micro. If you need to drive multiple digits it gets more difficult. The digit drivers will be that DC segment current * n * 8 for n digits.
– Spehro Pefhany
Aug 21 at 12:09
@SpehroPefhany I need to drive 2 digits, but I have plenty of spare IO on my atmega328p ;) I could use this as an opportunity to multiplex.
– mathieu
Aug 21 at 12:13
I've found that modern LEDs are a lot brighter than I think. I use 10k at 5V when breadboarding stuff and it's still plenty bright as an indicator (indoors, anyway). Except for yellow ones for some reason.
– immibis
Aug 22 at 2:40
Note that max current draw for Microcontrollers typically is two specs: per pin and total current limit. And, typically,
total != npins*max_per_pin– crasic
Aug 22 at 6:12