LM2907 shift lamp problems

[indecided]

Can you beg, borrow, steal or make a CMOS or 555 variable frequency square-wave oscillator to feed it then?
Test it without the engine running.

Hehe.. i assume u didn't see my message above posted 2 minutes before yours.

anyways...to recap, i fixed the problem, dirty Vcc, ignition.. changed to battery and it was all dandy.

however, i was wondering if you know a good way to regulate voltage in this case - as i use a LM741 with a resistor voltage divider network to get a voltage to compare to. when the loads are turned on, ths incomign Vcc 12v supply fluctuates, changing the shift point along with it.

in other words, when the air-cond/loads are turned on, the alternator produces more voltage, instead of 12v, it goes up to about 13.3++..that difference is what i mean.

any luck? hopefully a really small simple solution (like harnessing the 2907's op-amp) which i can't seem to figure out, like the speed switch

thanks!

 

[audioguru]

Hi Indecided,
Good, you've fixed your problem!
I have re-arranged your circuit a bit, and included zener regulation of the IC and shift-point. The LED will light at your set RPM point. I recommend an LED because it lights very quickly. An incandescent bulb draws up to 10 times its rated "hot" current when cold, and therefore may blow-up the transistor. Maybe that is why you were using a failure-prone relay.

 

[indecided]

Hi there audioguru..

just rebuilt the circuit with your changes..and volia..

the LM2907 blew up, righat across pin 11.

i thought a wire came loose, so i put another one in...

volia, it blew up again ;D at the same spot!

hmm..perhaps the 10k resistor at pin 5 which was removed should have been retained?

i'm not too sure, but the smell of fried sillicon wafting into my brain is sure a wakeup call for me

Hi Indecided,
Good, you've fixed your problem!
I have re-arranged your circuit a bit, and included zener regulation of the IC and shift-point. The LED will light at your set RPM point. I recommend an LED because it lights very quickly. An incandescent bulb draws up to 10 times its rated "hot" current when cold, and therefore may blow-up the transistor. Maybe that is why you were using a failure-prone relay.

 

[audioguru]

Hey Indecided,
It blew up? Twice?
What did you use for my suggested LED and its current-limiting resistor?
A piece of wire from the transistor's collector at pin 8 to the positive supply as it had before?

Wakeup call:
No current limiting = massive current = blow-up!

 

[indecided]

pin 8 is.. 680 ohms, i didn't have 570. and a nice water red LED.


ps : when i powered up the circut before starting the engine, the LED was on for the few seconds before the LM blew up.. doesn't that mean that the transistor is already switching it to ground?

Hey Indecided,
It blew up? Twice?
What did you use for my suggested LED and its current-limiting resistor?
A piece of wire from the transistor's collector at pin 8 to the positive supply as it had before?

Wakeup call:
No current limiting = massive current = blow-up!

 

[indecided]

pin 8 is.. 680 ohms, i didn't have 570. and a nice water red LED.


ps : when i powered up the circut before starting the engine, the LED was on for the few seconds before the LM blew up.. doesn't that mean that the transistor is already switching it to ground?

Hey Indecided,
It blew up? Twice?
What did you use for my suggested LED and its current-limiting resistor?
A piece of wire from the transistor's collector at pin 8 to the positive supply as it had before?

Wakeup call:
No current limiting = massive current = blow-up!

ahh! it was a wire shorting all along it works like a charm..a real charm!

appreciate your help so much audioguru! you've been invaluable..

thanks!

PS : are you good in car audio too?

 

[audioguru]

Hi Indecided,
Good, you have fixed your new problem!
Car audio? Sure.

 

[indecided]

Hi Indecided,
Good, you have fixed your new problem!
Car audio? Sure.

Yep..am sure excited to build my final production unit

one question..i substituted the 10k ohm pot for a 5k pot.

even then..i noticed that the range per notch ( i have a notched potentimeter) is about 500rpm... i was hoping to have accuracy to about 100-200rpm per notch... do u think i would get away with a 2-3k pot? would it have more precision? i don't really need the higher ranges...

 

[audioguru]

Hi Indecided,
The pot and the resistor in series with it form a voltage-divider to make a reference voltage from the 7.5V zener voltage. Keep your 5K pot and increase the value of the 10K resistor on its positive side to lower the indication to a lower RPM range. Also, you can add a resistor in series with the pot's negative terminal (now grounded) to increase the pot's RPM resolution.
I have re-designed the "RPM Adjust" so that now the pot will give nearly the same maximum RPM setting as before (how many RPMs was it?), and its minimum setting is half that RPM instead of zero RPM. Now it will have a setting of about 100 RPM per notch.
With finer resolution of RPMs comes with it a finer indication of the change of the zener voltage with supply voltage changes. If you see that the RPM indication changes with the electrical load on the alternator, then the zener must be changed to a voltage regulator IC such as the small UA78L08Z.

 

[indecided]

Ah..having a lil problem getting the exact range and resolution i want

just to get this straight, if i increase or decrease the 4.7k resistor, should my resolution drop or increase?

my plans are for a range from 2500 - 6500 or less...

Hi Indecided,
The pot and the resistor in series with it form a voltage-divider to make a reference voltage from the 7.5V zener voltage. Keep your 5K pot and increase the value of the 10K resistor on its positive side to lower the indication to a lower RPM range. Also, you can add a resistor in series with the pot's negative terminal (now grounded) to increase the pot's RPM resolution.
I have re-designed the "RPM Adjust" so that now the pot will give nearly the same maximum RPM setting as before (how many RPMs was it?), and its minimum setting is half that RPM instead of zero RPM. Now it will have a setting of about 100 RPM per notch.
With finer resolution of RPMs comes with it a finer indication of the change of the zener voltage with supply voltage changes. If you see that the RPM indication changes with the electrical load on the alternator, then the zener must be changed to a voltage regulator IC such as the small UA78L08Z.

 

[audioguru]

Hi Indecided,
What are the shift point RPMs now, using the circuit that I sketched, that had 20K at the top of your 5K pot and 4.7K at the bottom? I need to know what the shift point RPM is with the pot set to its maximum, and also with it set to minimum.

If you change the value of the 4.7K resistor to 10K, the minimum pot setting will increase to 1.8 times what it was with 4,7K. But the maximum pot setting also increases 1.3 times.
Then you can change the 20K resistor to 30K, to bring down the maximum pot setting to near what it was originally, and the minimum pot setting also drops, so that it is 1.5 times what it was originally. Therefore you will end up with 2/3 of the number of RPMs between steps in the pot.

 

[indecided]

Audioguru,

utilizing a 5k ohm resistor (actually i cheated and played with a 6.4k pot)
i got these figures = (stable at 4.98k) Min = 2400RPM Max = 5300RPM.

at the current moment, the 5k pot for RPM adjust has its resolution too narrow.. i would like the 5k to be able to cover 2400RPM all the way to 6400/7400RPM.

from your calculations, it appears that the resolution is becoming finer and finer. I think..i need a wider range as above. Should i try decreasing the 20k resistor instead?

thank you!

Hi Indecided,
What are the shift point RPMs now, using the circuit that I sketched, that had 20K at the top of your 5K pot and 4.7K at the bottom? I need to know what the shift point RPM is with the pot set to its maximum, and also with it set to minimum.

If you change the value of the 4.7K resistor to 10K, the minimum pot setting will increase to 1.8 times what it was with 4,7K. But the maximum pot setting also increases 1.3 times.
Then you can change the 20K resistor to 30K, to bring down the maximum pot setting to near what it was originally, and the minimum pot setting also drops, so that it is 1.5 times what it was originally. Therefore you will end up with 2/3 of the number of RPMs between steps in the pot.

 

[audioguru]

Hi Indecided,
I don't know which resistors that you used to record 2400min/5300max RPM, so I can't calculate values anymore.
If you reduce the value of my 20K resistor, then the max RPM point will go up. Try shorting it to see how high it goes.
Are you using a notched 10K pot, or a 5K pot?
What value resistor do you have from pins 3/4 to ground?

 

[indecided]

Audioguru, i used

5k OHM on pin 12 (your stated 4.7k), RPM adjust = 5K (Non-notched POT), 20k at pin 9. everything is the same per sept 7/04 diagram except 4.7k is 5k.

On pin 3/4 to ground, i have 100k (for 4 cyl)

perhaps u could show me how to calculate the values.. to make the pot respond to a wider range of frequencies. currently it's very very sensitive.. it's like every small bit i move is 50rpm...it's too detailled

Hi Indecided,
I don't know which resistors that you used to record 2400min/5300max RPM, so I can't calculate values anymore.
If you reduce the value of my 20K resistor, then the max RPM point will go up. Try shorting it to see how high it goes.
Are you using a notched 10K pot, or a 5K pot?
What value resistor do you have from pins 3/4 to ground?

 

[indecided]

Hi Audioguru,

after tinkering today..i find that my maximum range is still 3000rpm... what should be done in order to increase it to 4000/5000rpm? ie 2000 - 6000/7000...

Audioguru, i used

5k ohm on pin 12 (your stated 4.7k), RPM adjust = 5K (Non-notched POT), 20k at pin 9. everything is the same per sept 7/04 diagram except 4.7k is 5k.

On pin 3/4 to ground, i have 100k (for 4 cyl)

perhaps u could show me how to calculate the values.. to make the pot respond to a wider range of frequencies. currently it's very very sensitive.. it's like every small bit i move is 50rpm...it's too detailled

Hi Indecided,
I don't know which resistors that you used to record 2400min/5300max RPM, so I can't calculate values anymore.
If you reduce the value of my 20K resistor, then the max RPM point will go up. Try shorting it to see how high it goes.
Are you using a notched 10K pot, or a 5K pot?
What value resistor do you have from pins 3/4 to ground?

 

[audioguru]

Hi Indecided,
A formula for calculating resistor values for your shift point is not available because the resistors on each side of the pot affect each other, and we don't know the actual values of the cap at pin 2, the resistor at pins 3+4, your pot and the accuracy of your tach.
For example, you say that the lower resistor is actually 4.98K, but your RPM numbers make sense only if your pot is actually 6K, not 5K.

You say that you want a wider range of RPMs for the pot, but that a 3000 range is too sensitive to set accurately. The wider the range, the more sensitive the setting, unless you use a 10-turns or more pot. Why do you need such a wide range? It is either high RPMs for quick acceleration or low for fuel economy.

I have re-calculated resistor values:
27K from 7.5V, then your 6K pot, then 15K to ground. The shift point setting will nearly have a range of 2000 RPM and should be 4670 for minimum and 6540 for max. It will be easier to set than the previous 3000 RPM range.

 

[audioguru]

And re-calculating for a wide range so that each pothole will change the setting a few hundred RPM:
10K from 7.5V, then your 6K pot, then 2.4K to ground. It should be 1950 for min and 6820 for max.

 

[indecided]

Thank you very much audioguru!

the reason why i asked for a wider range is because previously with 2400-5300RPM range, i still had to turn quite a bit of the pot to go up 100RPM..i felt it was to detailled then.

Really appreciate your help! i'm also incorporating a 7808/78L08 into the circut because i find that the voltages are really unstable, causing the shift point to have an accuracy only to +-300RPM at the moment.

And re-calculating for a wide range so that each pothole will change the setting a few hundred RPM:
10K from 7.5V, then your 6K pot, then 2.4K to ground. It should be 1950 for min and 6820 for max.

 

[synchro]

hi, indecided.

Im having the same problem that you have had.
I was wondering if you could upload a diagram of the shiftlight that finally worked for you.
Im trying to make it work, but I don't why it doesn't.
I have a 4 cylinder engine too.

thanks

 

[Sig239]

Hello synchro,
From now on before you post you should look at the date of the post you are responding to. In this case it was two years ago.he he Anyways welcome to the forum, I'm sure you will find the help you need here, just start a new thread. BTW thanks for checking the old threads for the answers first though.