General > General Technical Chat

Low cost, low power consumption (<30ma) 2 digit 7 segment displays?

(1/2) > >>

comox:
Hi y'all,
I've been lurking on the EEVBlog site and forum for some time now, and I am now seeking advice/recommendations for a display requirement I am trying to satisfy.

I am developing a timer product and I need to display 2 digits to the user.   A dual-digit 7-segment display would satisfy the requirement; however, I am trying to keep power consumption and cost to a minimum.   Specifically, the 2-digit display should not consume more than 20ma to 30ma.  Normally I would consider a small 2-digit 7-segment LED display, but the power consumption of a bog-standard 7-segment LED display would greatly exceed the power restrictions.    To give you an idea of a 7-segment LED display that would satisfy the display requirement, check out: http://www.avagotech.com/pages/en/led_displays/surface_mount_seven_segment_displays/0.28_dual_digit_series/

I am also looking at 2 or 2.5 digit LCD displays, including one from Lumex http://www.lumex.com/products/detail/25_digit2 and another from Varitronix (VI-201) http://www.varitronix-hk.com/index.php?pid=2  I am planning to drive the LCD with an NXP PCF8566 which satisfies another requirement, in that I need to control the display via I2C.

Clearly the LCD display will operate with minimum power consumption; however, I would prefer the bright intensity of an LED display.    I have already placed an order with Digikey for the above NXP display driver and the LCD modules, and I have various 1 and 2 digit 7-segment displays on hand already.

Does anyone have any suggestions for an inexpensive 2-digit display that consumes a minimum amount of power?

Comox

alm:
If you can live with lower brightness, you might be able lower the current, although I doubt that regular LED 7-segment display will emit much light with all segments enabled at 30mA. You should use a switching/PWM-type constant current source for the LED's, not simple resistors. Depending on your input voltage, this might allow you to deliver a lot more current. The visibility of LCD sucks in the dark (unless you have a backlight), the visibility of LED sucks in bright light. So it depends where your product will be used. Is a backlit LCD module an option? Backlight should be possible below 20mA if it's LED.

NiHaoMike:
Most blue LEDs are very bright for a given current. (Even after accounting for the higher voltage drop.) The blue LED in my homemade iPod cradle is too bright to look at directly at just 5mA. ( http://ecorenovator.org/forum/appliances-gadgets/984-allie-moore-ihybrid-40-next-generation-ti-hybrid-digital.html ) Finding a 7 segment display that uses them, however, is a little difficult.

tecman:
If you can live with a passive (no light source) LCDs can run under 1 mA.  If you need an LED, most new displays with high efficiency LEDs will give a reasonable output under 5 mA.  Mux'ing the display digits keeps the draw low with LEDs.  Reds have the highest output for a given current, but abler is more visible/readable compared to red or green.  Just how the human eye works.

Your request is not difficult.

paul

mikeselectricstuff:
Low-current HE red displays can be readable at around 2-3ma per segment. All depends on your ambient light level. Best brightness/current is probably white but not cheap.
Obviously smaller displays tend to have better visibility at lower currents. Best bet is to order a selection and test them. Remember you can also often improve visibility with a tinted display filter to improve contrast.
20-30mA avarage for 2 digits should be easily doable.

Navigation

[0] Message Index

[#] Next page