7 Segment CC Brightness. - Page 1
Forum section: electronics / general

author: chinoy
author_rank: Regular Contributor
timestamp: November 10, 2023, 08:15:14 am
content: I have a small 7 Segment display. With a PIC and a Decoder chip. It uses 4 x Common Cathode displays. Part number RCC056CC.And we used BC639 as a switching transistor. This cant handle 1.5 Amps if I remember right. Which is more than enough for lighting up all the segments.Before people start asking for full schematic and pictures.I just need to know how the brightness of seven segments are marketed i.e. which parameter in the data sheet I need to be looking at.The complete circuit works on a 5 volt rail.What I have noticed is that every time I buy a new batch of seven segments the brand and part numbers change so does the brightness.For each new brand or make of CC 7 segment I get we will normally tweak the resistor values to get the highest brightness our of it.Some times 560 Ohms works sometimes 400 Ohms.Ideally Id just like to identify a seven segment CC that has the highest brightness out of the box. There seem to be huge variations between makes and brands.So what is that parameter I need to be looking at in the datasheet. And are there any tricks or tips to make the display more visible in day light other than putting it in a box with a black tint.I also noticed that the background color of the display cube changes from company to company. Some are white others are various shades of grey. Im wondering if I paint these black if it would help. Obviously I would need to ensure I don't get any paint on the led.Ps: I did do a search and also asked AI. This is what AI said.The brightness of a 7-segment display is primarily determined by the amount of current flowing through the LEDs (light-emitting diodes) within each segment. Here are the key factors that influence the brightness of a 7-segment display:Forward Current (If):Each LED within a 7-segment display has a specified forward current (If) that determines the optimal amount of current required for it to emit light at its maximum brightness. Exceeding this forward current may result in increased brightness, but it can also lead to accelerated degradation and reduced lifespan of the LEDs.Forward Voltage (Vf):The forward voltage (Vf) is the voltage required to turn on an LED and allow current to flow through it. The voltage across the LED should be within the specified range for proper operation. It's crucial to provide the correct voltage to achieve optimal brightness.Duty Cycle:The duty cycle is the ratio of time the LED is on to the total time of a complete cycle. For multiplexed displays, where each segment is illuminated sequentially, the duty cycle affects the perceived brightness. A higher duty cycle (more time on) generally results in increased perceived brightness.Multiplexing Technique:In multiplexed displays, individual segments are turned on one at a time in rapid succession. The overall brightness depends on how often each segment is illuminated. Higher multiplexing frequencies can contribute to a brighter display.Brightness Control Resistor (Rb):Many 7-segment displays include a brightness control pin (often labeled as "B" or "Br") that allows you to adjust the overall brightness by varying the resistance connected to this pin. By changing the current flowing through the LEDs, you can control the display brightness.Ambient Light Conditions:The ambient light conditions in the environment where the display is situated can affect its perceived brightness. In well-lit environments, a display may appear less bright compared to a dimly lit room.LED Efficiency:The efficiency and quality of the LEDs used in the display play a role in determining brightness. Higher-quality LEDs with superior light-emitting characteristics tend to produce a brighter and more consistent display.Temperature:The operating temperature can impact LED performance. Some displays have temperature-dependent characteristics, and extreme temperatures may affect the overall brightness.It's essential to follow the manufacturer's specifications and guidelines when designing or using a 7-segment display. Exceeding recommended current values or voltage limits can lead to premature failure of the LEDs. If you have control over the display brightness, adjusting the brightness control resistor or duty cycle can provide a means of optimizing visibility while considering power consumption and LED longevity.

author: Dan123456
author_rank: Regular Contributor
timestamp: November 10, 2023, 09:49:45 am
content: I just check the data sheet from one of the ones I have and it has a whole section on luminous intensity measured in ucd.https://www.vishay.com/docs/83180/tdcx10x0m.pdfI would assume that means they test for that but not sure if all 7 set displays are like that though.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: November 10, 2023, 02:18:10 pm
content: Even when manufacturers give figures for luminous intensity in mCd, it can still be difficult to compare because the figure will be given for a specific forward current, which can differ depending on what the manufacturer feels like using. Like, some will specify at 20mA, some at 10, etc. So you have to do a mental interpolation. Very annoying.

author: tooki
author_rank: Super Contributor
timestamp: November 10, 2023, 02:26:32 pm
content: Quote from: HwAoRrDk on November 10, 2023, 02:18:10 pmI think that’s an artifact of modern LEDs getting so efficient that the traditional 20mA current is simply too bright for many modern LEDs. (An early-1980s lime green LED is just visible indoors at 20mA. A modern emerald green LED at 20mA is retina-searingly bright — and reaches similar brightness to the 1980s LED at 20mA, but at just 0.5mA or so!)And it’s hard to “interpolate” the brightness since LED brightness vs drive current is highly nonlinear.

author: rdl
author_rank: Super Contributor
timestamp: November 10, 2023, 02:27:51 pm
content: You're going to have ongoing problems unless you can switch to a supplier that can sell you the same part every time.