problems getting M74HC259B1R to work

[777xxx]

im trying to get it to latch at address 0 to output 0. no joy. the light just stays on and when i press the button, it gets brighter. no on off latch. whats wrong here? any ideas?

 

[Tony Stewart]

Everything’s wrong. Start with a more accurate schematic with part numbers , correct polarity, bias resistors , no floating inputs , and a better question

 

[sagor1]

Also remember that 74 series can only source or sink so much current, and you have no current limiting resistor. Good way to blow something.

 

[777xxx]

Everything’s wrong. Start with a more accurate schematic with part numbers , correct polarity, bias resistors , no floating inputs , and a better question

ok. is there a circuit diagram anywhere that i can look at which allows me to use this chip as a latch with press button switch?

 

[ZipZapOuch]

ok. is there a circuit diagram anywhere that i can look at which allows me to use this chip as a latch with press button switch?

The datasheet is usually a pretty good place to start (along with a basic understanding of ohms law so you don't exceed the specified max current in/out of any pins.

https://www.st.com/content/ccc/resource/technical/document/datasheet/e1/c4/50/bf/c3/bf/4d/ac/CD00000290.pdf/files/CD00000290.pdf/jcr:content/translations/en.CD00000290.pdf

 

[777xxx]

The datasheet is usually a pretty good place to start (along with a basic understanding of ohms law so you don't exceed the specified max current in/out of any pins.

https://www.st.com/content/ccc/resource/technical/document/datasheet/e1/c4/50/bf/c3/bf/4d/ac/CD00000290.pdf/files/CD00000290.pdf/jcr:content/translations/en.CD00000290.pdf

yea, i have looked at the datasheet already but still having problems getting it to work

 

[audioguru]

Your sketch has no button nor Enable and Clear wire connections.

 

[777xxx]

Your sketch has no button nor Enable and Clear wire connections.

yea it does. just click on the image. i tried wiring up the enable and clear to ground but it made no difference

 

[Tony Stewart]

1. Observe all antistatic precautions
2. Never leave CMOS inputs floating. Either pull up or down.
3 Place a ceramic cap near IC V+ to gnd
4. Latch Enable =0 must be enabled.
5. Clear must be disabled = 1
6. Output is immediate until Enable = 1 then it is latched in to register.
7. Then ABC address select = 000 to observe output on Q0 = 0 LED off = 1 ON
Your LED is backwards if grounded.
Vcc must be 5V +10% max.

 

[777xxx]

1. Observe all antistatic precautions
2. Never leave CMOS inputs floating. Either pull up or down.
3 Place a ceramic cap near IC V+ to gnd
4. Latch Enable =0 must be enabled.
5. Clear must be disabled = 1
6. Output is immediate until Enable = 1 then it is latched in to register.
7. Then ABC address select = 000 to observe output on Q0 = 0 LED off = 1 ON
Your LED is backwards if grounded.
Vcc must be 5V +10% max.

View attachment 145082
View attachment 145083

thank you for your diagram. i dont understand what you mean when you say 'led is backwards when grounded'. in my diagram the positive lead is connected to the data output and the negative is attached to ground. is this wrong then?

 

[Papabravo]

thank you for your diagram. i dont understand what you mean when you say 'led is backwards when grounded'. in my diagram the positive lead is connected to the data output and the negative is attached to ground. is this wrong then?

It is absolutely WRONG! The output would have to be negative (below GROUND) in order to provide a positive (forward) bias to the diode. You also need a current limiting resistor in series with the diode.

 

[audioguru]

Yes, your LED is backwards. Lookup "LED".

 

[777xxx]

Yes, your LED is backwards. Lookup "LED".

ah yes i see now. i googled anode and it said negative. i did put the led in the correct way round on the board, though

 

[ZipZapOuch]

...i did put the led in the correct way round on the board, though

That's way more important than the drawing.

 

[777xxx]

1. Observe all antistatic precautions
2. Never leave CMOS inputs floating. Either pull up or down.
3 Place a ceramic cap near IC V+ to gnd
4. Latch Enable =0 must be enabled.
5. Clear must be disabled = 1
6. Output is immediate until Enable = 1 then it is latched in to register.
7. Then ABC address select = 000 to observe output on Q0 = 0 LED off = 1 ON
Your LED is backwards if grounded.
Vcc must be 5V +10% max.

View attachment 145082
View attachment 145083

its not working unfortunately. the light comes on when i press the button but it doesnt latch

 

[tumbleweed]

Look at the truth table. It's not going to latch until ENABLE is set high.

 

[777xxx]

Look at the truth table. It's not going to latch until ENABLE is set high.

this is not what i really want. i want it to latch without having to hold another button. if i just push the enable high button and release it, the data is lost

 

[Tony Stewart]

Then you are using the wrong chip. This is a Latch with Data thru enable Low

which means disable high = memory latch

You want a different design that is edge sensitive to inputs but then there must be some read and reset function added.

 

[777xxx]

Then you are using the wrong chip. This is a Latch with Data thru enable Low
View attachment 145134 which means disable high = memory latch

You want a different design that is edge sensitive to inputs but then there must be some read and reset function added.

its ok ive sorted it, im using 2 nand gates. although i do have to keep pressing the buttons quite alot to get it to change