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ADC0808 problem

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siau2

New Member
Hi all,

I refer to this circuit to build my ADC0808 in free-running mode.

However, for the clock, I'm using the frequency generator at first for frequency about 500 kHz but it's not working. Then I tried use 555 timer in astable mode, and it still not working.

Now I wonder the problem is with the circuit or with the clock. Any opinion?
 

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Roff

Well-Known Member
I agree with Panic Mode. In addition, your schematic doesn't have pin 16 on it. It needs to be grounded.
 

siau2

New Member
Hi,

Thank you for the advice. For the pin 16, it is grounded anyway in the schematic. The writing of number 15 and 16 looks similar.
 

najeeb

New Member
siau2 said:
Hi all,

I refer to this circuit to build my ADC0808 in free-running mode.

However, for the clock, I'm using the frequency generator at first for frequency about 500 kHz but it's not working. Then I tried use 555 timer in astable mode, and it still not working.

Now I wonder the problem is with the circuit or with the clock. Any opinion?

dont' panic, you can do it!
I too had problem with same ckt. But solved.
What i did is just adjusting the offset level of input voltage. Check the offset of input signal
Try to connect your ckt with a signal generator and CRO, you can solve it very easily.
 

Pawel

New Member
ADC0809 Problem

Hello

I have problem with adc0809. Values:

Vcc = 4.9V
Fclk = 100 KHz (Amplitude 5V)
Vref+ = Vcc
Vref- = 0V
Vin = I have tested many values below Vref+

I don't know how to check if my adc is no damaged. Najeeb, could you tell me values adc is working correctly?
If I connect SC (temporary) to ground I should reset my adc. There is no effect.
If I apply Fclk (frequency) all diodes light!
I check all connections they are good.
I'd like to manually reset adc, if I turn on/turn off Vcc there appears nonstability (diodes don't correspond to Vin) or my adc is damaged.
I need clear procedure how to test my adc.
 

plotoyee

New Member
hello
im facing the same problem same as u
infact im using ur circiut diagram.
can u tell me how u fix it??
thanks
 

udi_hakim

New Member
You cannot put leds directly to the ADC , you should make a pull down connection (put all the anodes of the leds in Vcc and when the adc outputs will turn low the leds will light up)
 

mnoman

New Member
how ADC works

Hello!

can any one help me that how I can apply clock to ADC0808 and of what frequency

waiting for reply

BYE
 

trevor261

New Member
Can't start a thread so I'll ressurect one

Hello all. This is my first post here, I require assistance with some analogue-to-digital circuitry. For my school project I am building a digital thermometer. An LM61 is connected to a ADC0808 whichs connects to an EEPROM which outputs BCD to 4511B's which drive 7-segment displays. While reading the datasheet for the ADC0808 I noticed that the output is Tri-State. Does this mean I need resistors branching off from the ADC's output to ground to prevent the EEPROM's address inputs from floating?
Also, would a 555 be suitable for providing the 10-640kHz required for the clock input on the ADC0808?
 

kchriste

New Member
Forum Supporter
While reading the datasheet for the ADC0808 I noticed that the output is Tri-State. Does this mean I need resistors branching off from the ADC's output to ground to prevent the EEPROM's address inputs from floating?
No. Just make sure that the Output Enable pin (OE) is high. This turns "on" the outputs. If OE is low, then the output pins are HiZ and will float without pullups.
Also, would a 555 be suitable for providing the 10-640kHz required for the clock input on the ADC0808?
The bipolar LM555 is OK up to about 100Khz or so. It won't work at 640Khz. I think the CMOS version of the 555 goes higher. I see no reason to clock the ADC really fast for a thermometer anyway as the temperature will change very slowly.
 
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audioguru

Well-Known Member
Most Helpful Member
Here I am reading posts from 2003. I was about to copy and paste parts of the datasheet then saw the very old date.

Maybe very old threads should be tinted red.
 

trevor261

New Member
What's wrong with 2003 datasheets?
This thread appears to have been resurrected several times over the years, I only used it because I can't start posts yet.
I thought that the 555 could provide up to 500kHz? Or is it that it can't produce the right oscillations I require at frequencies higher than 100kHz?
 

trevor261

New Member
So I can't just use a standard 555 timer? 100kHz would be suitable for my circuit, I won't be noticing the speed anyway.
 
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