Trouble Understanding The Schematics For ICL7106 Datasheet

[Rory Starkweather]

The datasheet I am looking at is
http://docs-europe.electrocomponents.com/webdocs/0118/0900766b801185ff.pdf

(I hope that came out as a link.)

Some people have already asked me why I care. Use a uProcessor. My only response is, "Which came first, the LED or commercially available uProcessors? There are actually some benighted souls who claim that it is not possible to use an LED or LCD display without a uProcessor.

Well, I'm having trouble figuring out where the uProcessor ends, and the display starts, so I want to go back to basics until I really understand them.

In Figure 1. Osc 1 - 3 are shown connected. (Pins 38 - 40) Does that mean that they are using the internal Oscillator for their frequency reference?

Kind of the same thing with Ref Hi and Ref Lo (Pins 36 and 35) It seems that what they have done is shorted Ref Lo to In-, Pin 30. Which kind of makes sense, but why is the input to Ref Hi (Pin 36) produced from two resistors, one variable? Is it necessary that Ref Hi be referenced to In Lo (Pin 30) instead of V- (Pin 26)? All examples show pretty much the same thing with different resistance values.

Figure 19 shows a configuration "Developing Under range and Over range signals." Naturally, since I'm paranoid and have no idea what I'm doing, I would like to implement these, but is this a separate IC? The OR/UR circuitry uses several of the segment control pins. Are the majority of the pins left unconnected in the drawing because this is a separate IC? It doesn't show any way to connect to the other IC if there is one.

Basically that concept confuses me.

In Figure 22 it shows a setup for buffering the output from the 7107, which is for LED displays. I haven't looked up the DM7407 yet, but I'll bet it doesn't have 21+ outputs. ??

See you all later.

 

[KrisBlueNZ]

In Figure 1. Osc 1 - 3 are shown connected. (Pins 38 - 40) Does that mean that they are using the internal Oscillator for their frequency reference?

Yes, they are using the two internal inverters in a standard CMOS oscillator configuration with one external resistor and one external capacitor, as shown in figure 9B on page 9. The external resistor and capacitor determine the frequency with moderate accuracy. The values suggested, 100 pF and 100 kΩ, give an oscillator frequency of around 48 kHz.

Kind of the same thing with Ref Hi and Ref Lo (Pins 36 and 35) It seems that what they have done is shorted Ref Lo to In-, Pin 30. Which kind of makes sense, but why is the input to Ref Hi (Pin 36) produced from two resistors, one variable? Is it necessary that Ref Hi be referenced to In Lo (Pin 30) instead of V- (Pin 26)? All examples show pretty much the same thing with different resistance values.

From a quick read of the data sheet, I think that the device is fully differential and it only cares about the voltage between REF HI and REF LO (provided that both pins are within its supply voltage range).

In the example circuit, VIN- and REF LO are both connected to COM, which is internally regulated by the ICL7106 or ICL7107 to about 2.8V less than V+ (see page 5 of the data sheet). So the resistor R1 and trimpot R4 are used to provide an adjustable fraction of this 2.8V "reference" voltage at REF HI (relative to REF LO). You would adjust R4 so REF HI is 100 mV higher than REF LO (assuming you want a 200 mV full scale). This is not the recommended way to generate a reference voltage because the 2.8V generated internally by the device is not very accurate (varies with temperature).

Figure 19 shows a configuration "Developing Under range and Over range signals." Naturally, since I'm paranoid and have no idea what I'm doing, I would like to implement these, but is this a separate IC? The OR/UR circuitry uses several of the segment control pins. Are the majority of the pins left unconnected in the drawing because this is a separate IC? It doesn't show any way to connect to the other IC if there is one. Basically that concept confuses me.

Those circuits show how to add underrange and overrange indication to the main ICL7106 or ICL7107. Other pins are connected as normal; the diagram only shows the extra connctions that are needed for underrange/overrange detection. The circuit seems to be monitoring the segment outputs to determine overrange/underrange but I haven't looked into the details.

There's a problem with the underrange/overrange circuit for the ICL7107. The LM339 quad comparator needs pullup resistors (e.g. 10 kΩ) on all of its outputs to be able to drive the CD4023/74C10 NAND gate IC.

The underange/overrange circuitry isn't needed; the device won't be damaged by moderate overrange - it will just indicate 1999 or -1999.

In Figure 22 it shows a setup for buffering the output from the 7107, which is for LED displays. I haven't looked up the DM7407 yet, but I'll bet it doesn't have 21+ outputs. ??

Correct. It has six buffers, so you would need four of them. And the 7407 is ancient and practically obsolete. You can still get them from Digi-Key, and the data sheet is available at http://www.ti.com/lit/ds/symlink/sn7407.pdf.

I think a better alternative would be an array of "pre-biased" or "resistor-equipped" transistors, one for each segment. The ICL7107's segment outputs are active-low, designed to drive common anode displays, so you need to use PNPs. Suitable transistors are the Fairchild FJN4301 (http://www.digikey.com/product-detail/en/FJN4301RTA/FJN4301RTACT-ND/4743945) (also available through Mouser) and some physically smaller devices from Panasonic which are not stocked by either Digi-Key or Mouser.

Connect the transistor with its base to the output pin on the ICL7107, its emitter to the +5V supply, and its collector through a current limiting resistor to the anode of the display segment. This requires a common cathode display instead of the common anode type that can be directly driven by the ICL7107.

There's quite a lot to learn about the ICL7106/7. There's a list of relevant application notes at the top of page 11 of the data sheet. I also Googled ICL7106 ICL7107 application information (you can do that too) and I got the following hits which should be relevant:

http://www.intersil.com/data/an/an023.pdf
http://www.intersil.com/content/dam/Intersil/documents/an05/an052.pdf
http://www.kitsrus.com/pdf/7106_an.pdf
http://ecircuit1001.blogspot.com/2009/04/icl7107-digital-led-voltmeter.html

 

[Rory Starkweather]

TYVM. You've been a big help to me here as well as elsewhere.

Let's see if I can post a link for a prehistoric "7 Segment LED" site.

http://www.electronics-tutorials.ws/blog/7-segment-display-tutorial.html

 

[KrisBlueNZ]

You're welcome. And that's a good tutorial you found there.