biboymusic
Member
I will check my local store this morning and look for those IC's. Thanks.
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Hi Eric,
I have searched every electronics store within my city and the nearest cities and only found the LM358 IC. No luck on CA3240 Dual OPA. I was about to buy the LM358 but then I realized that maybe there will be a change in the schematic if using the said IC. So I need a confirmation from you that LM358 is an exact replacement of CA3240 and they both can use the same circuit. If there are things to be changed (resistor & capacitor values) please tell me. Thanks and more power.
hi aljamri,
It is VB5, the exe file is on my Forum Blog.
https://www.electro-tech-online.com/blogs/ericgibbs/126-basic-lm3914-calculator-v3-1.html
@mneary, Im from the Philippines and on a quite outback city. TL072 is the only Dual OPA available here. Usually I order online, and ordering such very cheap IC will cost me more on shipping.
Hi Eric,
I just finished building the circuit using your schematic. However, it works strangely. Im guessing that the circuit I've used for the LM3914 is different from what you expect me to build. I'm using the test circuit from the LM3914 datasheet on page #2.
My bad eric. I didn't realize that the screenshot from your LM3914 is a schematic. Can you convert it to a standard schematic? I'm really not good with this but I'll try.
Pins #2 & #4 connects to the ground.
Pin #6 connects to Pin #7.
Pin #7 connects to Pin #8 thru a .75K resistor.
Lastly, Pin #8 connects to ground via .82k resistor.
Then +vo2 from LM358 connects to Pin #5 of LM3914.
BTW, I wrongfully bought electrolytic capacitors for C1, C2, & C3. Will this still work? I connected them based on the polarity of connections where the capacitors are placed except for C2 where I assumed that the (-) pole of the capacitor connects to the inverted input (-) #2 of LM358.
What capacitors did you buy that were wrong.??Pins #2 & #4 connects to the ground.
Pin #6 connects to Pin #7.
Pin #7 connects to Pin #8 thru a .75K resistor.
Lastly, Pin #8 connects to ground via .82k resist
On the Dual OPA schematic the C1, C2, C3 labeled capacitors I bought where wrong. I bought the correct values only that they are polarized (electrolytic) capacitors. I just realized now that they should be Mylar or film type (non-polarized) capacitors. Will still the circuit work?
hi,
Those caps should be OK, except the one across the second opa.
Ideally the 100nFs should be ceramic, the higher values are electrolytic.
hi,The 100nFs I bought were correct, ceramics (Nanos are so damn hard to find, went to another city 300km away and it only costs $0.21). C1 and C3 I guess would be ok with electrolytics since their polarity in the schematic are obvious. How will I connect C2 in the second OPA using an electrolytic? Or should I omit it? I connected it in a way that the (-) leg is on the inverted input of the second OPA and the (+) leg on vo2.
Hello,
I'm located in the Philippines on a quite outback city.
I just tested the completed circuit and here's the result. From full tank to empty, only 2 LEDs were affected the 8 other LEDs were just lit up.
How do i calibrate the circuit? should I trial and error the pots?
hi,Hi Eric,
I have a strange problem with the circuit. Varying the SPAN pot only gives me .10v to .65v, while varying the ZERO pot perfectly lights all 10 leds and turns them off @ 0-2.78v. I think there's something wrong on the OPA #1 setup, varying the fuel sender resistance doesn't do anything.
I also connected the 33K resistor (+vr) to the junction of the 2 470 ohms resistor that marks (+vr).
hi,
Good to hear that the LM3914 section working ok.
Measure these voltage points, let me know.
#1, Junction of the two 470R that feed the tank sensor [vr]
[ should be approx +4v]
Yes, it reads +4v
#2, Junction of the 470R and the tank sensor [vs]
[should be from 70mV thru 770mV, from full to empty]
Readings are only at 14mV @ full and 26mV @ empty
Note that R2 [10k] from the sensor is connected to pin #3 of the 1st OPA
Yes it is connected that way.
EDIT: make sure that R5 [4k7] on pin #2 of the 1st OPA is connected to 0V
Yes it is connected that way too.
I cant get to 1V on pin #1 of the OPA even by varying the SPAN pot.
Measure these voltage points, let me know.
#1, Junction of the two 470R that feed the tank sensor [vr]
[ should be approx +4v]
#2, Junction of the 470R and the tank sensor [vs]
[should be from 70mV thru 770mV, from full to empty]
Note that R2 [10k] from the sensor is connected to pin #3 of the 1st OPA
EDIT: make sure that R5 [4k7] on pin #2 of the 1st OPA is connected to 0V