# Best solution to use of 6" 6-digit 7-segment display the clock without multiplex

Hi,

What is other options to get display for the subject arrangement other that multiplexing.

As the big (like 6"/12") display using ULN IC alongwith Transistors for anode/cathode site each segment is of 2 stringS of 6 LEDS ) with multiplexing technique is not a solution of getting proper brightness.

Is there other technique to implement for this arrangemt??

tnx

Hi raj,

Used this string for each digit (2 string/segment), If-20ma, Vf-12 volts. and peak-30 ma.

As an Anode driver- ULN2003A (o/p current 500ma per driver pin) and BC327(collector current of 500mA).

As Cathod Driver- ULN2803(collector current 500ma).

Used 15v power supply.

For a 6 digit clock, the average current in the LED's will only be 30 mA / 6 = 5 mA

The peak current for one digit is then 7*2*30 mA + 1 * 30 mA = 450 mA

5 mA average in x6 mux may be too low for bright ambient light conditions.

Thus I believe this display will be best operated in non-mux.

Note: The complete ckt not in my hand right nw. I will pase hare early.

7-segment driver ICs.

>>Are u asking bcd-7segment driver max7219. that means 6 max7219 is req. One for each digit. Is there any link for ckt  diagram combination with my reqirement and can u provide that link for my knowledge gain. Although I am not going to implement my case with max7219 ic.

Tnx/

Joined October 05, 2018      8
Friday at 07:49 PM

Helooo all....Nice to meet u....

I have download program to STM8s103f3 using IAR throught ST-Link. There is no error while debug and download, but after this chip have applied to the DSN-VC288 board, it was not working. What's the problem ???

Joined August 21, 2021      1
Saturday at 06:35 PM

According to the datasheet, the decimal point uses one string of  LEDS, and all the other segments use two parallel strings.
I think this means that the peak current for the segments is 60 mA, 30 mA in each string.
The peak current for one digit is then 7*2*30 mA + 1 * 30 mA = 450 mA

As a power supply unit to drive all the 6 digits, I want my own unit which is combination of Bridge rect, Filter cap, ic LM7815 arrangement only.
But what should be transformer (for 230/15v) amp rating for driving all 6 digits:

For testing purpose, i tested 2 digits with 230/15v 1 amp transformer but the trf. got damaged, where as a single digit worked correctly with the same 1 amp trf.

Question No: 1))>> Why trf got damaged while used 2 digit. As were requred 450*2 =900mA.

Question no 2:>> will be that for 6 digit, 450 mA * 6 Digits = 2700 mA (+ additional 20%) = 3240 mA
So Should I need to use the TRF of MORE THAN 3240 mA for sec 15V for all 6 digit (as this CURRENT will not available at market with 15v trf. , but with this calculation I wanted to drive 2 digits with 230/15v of 1000 mA trf only for testing purpose and same trf pr. side got burnt/open

OR, 15V 4A SMPS - 60W - DC Metal Power Supply, and if not available in local market then should i
18V 4A SMPS - 72W - DC Metal Power Supply.

TNX..

Joined October 05, 2018      8
Friday at 07:49 PM

Are you sure with your calculation that a single 7-segment display uses 450mA. If yes then I guess it should be a big display board. So yes, for 6 digits you will need about 2.7A which quite a big value.

I would suggest you to buy an SMPS with 15V 5A rating to power your entire circuit. Use a transformer to power your project is not a good idea beacuse of the large current value and abviously SMPS will be cheaper than buying such a bulky transformer and designing the regulator on your own.

I want my own unit which is combination of Bridge rect, Filter cap, ic LM7815 arrangement only.

Any particular reason to built your own circuit? Also microcontrollers are noise sensitive, so if you are builting your own power regulator make sure it is noise free else you will get weired results.

For testing purpose, i tested 2 digits with 230/15v 1 amp transformer but the trf. got damaged, where as a single digit worked correctly with the same 1 amp trf.

There could be multiple reasons for this. But when you draw too much current (overload) from a transformer it likely will get hot and will fail only after prolonged use. Did you notice any of these heating issues. If not the reason for failure could be something else. Also most transformer that we get from hobby store does not live up to the original current rating mentioned on their spec sheet.

Also what is operating voltage of your design? Is it 15V, if yes why?

Joined May 19, 2015      213
Tuesday at 03:45 PM

Are you sure with your calculation that a single 7-segment display uses 450mA. If yes then I guess it should be a big display board. So yes, for 6 digits you will need about 2.7A which quite a big value.

Yes it is big like 6 inch disp. and refer to leds' string in my post here on "June 1, 2019 - 7:03pm" datasheet mentioned forward current 30ma and volt 12v.

so my calculation refer to that,  The peak current for one digit is then 7*2*30 mA + 1 * 30 mA = 450 mA.

Also what is operating voltage of your design? Is it 15V, if yes why?

As the drop is 12 v, for current regulation the design volt is 15v with current limit resistor.

I would suggest you to buy an SMPS with 15V 5A rating to power your entire circuit. Use a transformer to power your project is not a good idea beacuse of the large current value and abviously SMPS will be cheaper than buying such a bulky transformer and designing the regulator on your own.

I tried to make all the things with my own including power supply.

But why 5Amp you are recommending here? why not 3.2Amp OR above 2.7Amp as calculation revealed? >> Any resons please.......

There could be multiple reasons for this. But when you draw too much current (overload) from a transformer it likely will get hot and will fail only after prolonged use. Did you notice any of these heating issues. If not the reason for failure could be something else. Also most transformer that we get from hobby store does not live up to the original current rating mentioned on their spec sheet.

Yes may be spec issue, as i required 2*450=900mA (2 digit) but spec is 1000mA and may also below rated.

The heat was not noticed while damaged. both digit stand only a second with blinking. What could be the cause??

So what volt and current will fit for it??

tnx

Joined October 05, 2018      8
Friday at 07:49 PM

As the drop is 12 v, for current regulation the design volt is 15v with current limit resistor.

So are you using a shunt method to measure the current? 3.2A is a big value you will be needing a high wattage resisisotr and will loose a large drop againt it. If you are not concerned about power effeciancy then it is still fine.

But why 5Amp you are recommending here? why not 3.2Amp OR above 2.7Amp as calculation revealed? >> Any resons please.......

Yes you can use the 3.2 or 3.4 version SMPS as well. The reason I suggested 5A is that it is commonly availabe. If you able to find a smaller version for a better price you can use it.

Yes may be spec issue, as i required 2*450=900mA (2 digit) but spec is 1000mA and may also below rated.

The heat was not noticed while damaged. both digit stand only a second with blinking. What could be the cause??

So what volt and current will fit for it??

I have busted a lot of transformers over the years and everytime I overload it they would heat before going dead. also you can use a multimeter to check for connectivity between the primary and secondary terminals to find out which side coil has burt out. To find the actual reason you would have to load the transformer with a variable load and monitor its output current. Then you can make sure if you transformer is operating at 1A.

Joined May 19, 2015      213
Tuesday at 03:45 PM

Drive LED of the display with a constant current source.

Joined February 12, 2018      696
Monday at 02:11 PM