Stumped :-( large voltage drop and logic not working - Analog electronics :-)

[ebclr]

As the colleague wrote  figure 7 is the key to solve your problem you will need a bunch of resistor to limit the current, this will reduce the current  to a specified level and probably the 5V power supply will be ok

Try that sugestation

[Chris Mr]

It does say at figure 7 that current limiting resistors are required but that is only for the 5082-7304 - it says so in bold above figure 7.  In addition, all that part of the data sheet refers specifically to the 7304 - truth table, package dimensions etc all in one place.

The 5082-7304 is the '+','-','.','1' left hand "over range display" digit whereas the other devices are for standard numbers.

The 7300 has the decimal point at the right hand side, the 7302 a the left hand side and the 7340 doesn't have a decimal point - it has a blanking input instead - and does hexadecimal characters too.  The 7300, 7302 and 7340 must be current limited internally.


Could it be the OP has used the 7304 in one (or more?) of the positions because when 'on' the two LEDs in series will have a voltage drop of 4v - and no current limit - and that's what's being reported.

[ebclr]

You are right

Try to drop everything.

And put only one display and measure the voltage and current on power supply please

[Chris Mr]

Just to clarify from the data sheet.

At the top of the first page it says "Includes Decoder / Driver" (fourth bullet point) but does not mention the 7304 - that is a separate device which is discussed separately.

[ebclr]

What is the exactly device you are using ?

[eetech00]

If the OP wishes to display numbers, the LED display should be the numerical display 5082-7300.

Either way, the circuit is driving the LED Displays with a 74LS192. The 74LS192 cannot supply enough current to directly drive the LED displays. Need external transistor drivers like Figure 7.

[ebclr]

http://www.ne.jp/asahi/shared/o-family/ElecRoom/PARTS/DISPLAY/HP7300a.jpg

If you are using this device on the picture, they have the driver inside

PLease confirm are you using this one ?