audioguru

Hi Max,
Most parts with a dedicated part number are the same from various semiconductor manufacturers, so that companies that make stuff can get "second sources" when their favourite manufacturer runs out of stock. However, some oriental semi manufacturers make an "improved" copy, sometimes with disasterous results! (New Japan Radio's NJM072 copy of a TL072 has "improved" extra wide bandwidth. But it oscillates like crazy and cannot be used in low-gain circuits. They quickly replaced it with their recommended NJM072B).

I would choose National Semi's LM3914, because they invented the thingy and have been good to me. It may cost a little more than ON Semi, Fairchild or others.
I would also order National Semi's LM555.

I haven't yet calculated the resistors in the current source. I will do so soon.

Maxer

i didn't quit understand this statement... there is no resistor in IC555 circuit.... I think you may have changed you original circut because i don't know what resistor you are talking about in LM3914 either.
but will the internal delay of 555 will discharge cap completely? if not we have to add cap and resistor to pin 2 and 6 and then ground? to add a delay of our own.. or will the internal delay of IC555 will work?

Maxer

Also there are different types of LM555 and LM3914 IC from Semi national here is the list pick 2 so i can pick the correct once. thanks
http://www.national.com/pf/LM/LM555.html
http://www.national.com/pf/LM/LM3914.html

audioguru

Hi Max,
Clarification:
1) Of course the ICs have resistors inside. The LM3914 has a bunch of resistors between pins 4 and 6 that determine what input voltage lights its LEDs, and the 555 has resistors that determine the lowest and highest voltages of its timing cap.
2) Of course the circuit has changed from my original one, now the 1uF cap is the 555's timing cap, which never discharges to ground like it did in my circuit.
3) Inside the LM3914 between pins 4 and 6 are 10 resistors in series, that are used as a voltage divider. This voltage divider determines what input voltage turns on the LEDs. Now that the 1uF cap is used as the 555's timing cap, the cap's voltage will range from 1/3 of the supply voltage for its discharged voltage, to 2/3 of the supply voltage for its highest voltage. The 555's 1/3 and 2/3 of the supply voltage reference points are determined by a voltage divider of 3 resistors inside the 555 that are connected between the supply and ground.
4) We must duplicate the 555's voltage divider with another voltage divider for the LM3914 so that the 1st LED lights when the cap's voltage (input to the LM3914) is 1/3 of the supply voltage (the cap is discharged by the 555) and the 6th LED lights when the cap's voltage is a little less than 2/3 of the supply voltage (cap is at its highest voltage). It would be a lot easier to calculate voltages if the 555's cap voltage simply ranged from ground to a fixed voltage. It would also be a lot easier if you had 10 LEDs instead of only 6.
5) The 1st scan is longer because the cap must charge from zero volts (fully discharged from the circuit being unpowered) to 1/3 of the supply voltage before the timing actually begins. The LEDs will be off during that time.
6) You must measure the LM3914's voltage divider total resistance between pins 4 and 6 because the datasheet says that it could be anywhere from 8K to 17K ohms. We must know exactly what it is.
IC's are lousy at making accurate value resistors, but can make very accurate duplicates and ratios that are used in "normal" LM3914 and 555 circuits.

BTW, the emitter of the 2N3906 current source and its resistors must now connect to the supply voltage, instead of to the LM3914's pin 7. Pin 6 must also be disconnected from pin 7. Pin 4 must be disconnected from ground.

audioguru

Hi Max,
You need an LM555CN and an LM3914N-1.
They are normal size plastic case DIL ICs for soldering their pins through holes in a circuit board.
The other packages are metal or ceramic for military or outer-space uses, are bare chips or are tiny little things which are usually soldered on top of a circuit board (surface-mount) by robots.

Maxer

what if we change the 1uf cap to .1 uf? it would discharge quicker

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audioguru

Hi Max,
Sure 0.1uF would discharge quicker. 0.01uF or 0.001uF would be even quicker! 100 puffs (slang for picoFarads)? or just 10 puffs?

In order for the timer's period to be about 1 second per scan, the capacitor's charging current must be low. The time calculation is roughly one divided by the current, times the capacitor's value. So if you reduce the value of the capacitor then the charging current must also be reduced by the same amount.
The problem with having a very low charging current is that pins 2 and 6 of the 555 need a small current to operate, and may steal all of the very low charging current, leaving the capacitor with nothing. Actually, the currents for pins 2 and 6 are opposing, so that the current required by pin 6 can be supplied by the current from pin 2. The datasheet spec's a current for pin 2 but not for pin 6, so maybe they are not equal.
Since the current for pin 2 is spec'd with a wide range, I wouldn't risk operating the 555 with a very low charging current and would stay with using a 1uF (low-leakage metalized poly) cap.

Maxer

internal delay of IC555 that will discharge cap much less then 1/3 Since the cap is now shorten threw pin 5 of ic555... If you think this schematic looks allright and no other modifications are needed please identify tha values of all resistors, my specs for LED's are posted above.... at least 20mA per Led would be good
thanks again
max

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audioguru

Hi Max,
Are you saying that the 1uF cap will be discharged so quickly that its voltage will overshoot the 1/3 of the supply voltage that triggers pin 2, because the internal delay of the 555 will release the discharge transistor at pin 7 too late?
It could be, but I don't think the capacitor's discharge voltage will overshoot much. If it does, the voltage level for the 1st LED to light can be adjusted to be the same voltage.

Why do you have a resistor to ground at pin 5 of the 555?
It would just lower the capacitor's maximum charge voltage directly, and lower the cap's minimum voltage half as much.

Maxer

well if using ref voltage of LM3914 v have to lower voltage of 555 too.
added modification of res to pin 5 of 555. so now i have to know which pins are on when cap is charging... and add led's to those pins since there's only 6 leds.. what are the values of the resistors and pot you added??
I could be wrong but i want to order these parts from all one place....
so here is the list for 1 circuit board.
6 Leds
1 LM3914 IC
1 LM555 IC
1 18 pin socket
1 8 pin socket
1 capacitor 100uf/25V
6 270ohm resistors
2.7K ohm resistor
620 Ohm resistor
transistor 2N3906
2 capacitors .01 uf/25v
Experimental soldering board
-------
parts not sure about
1UF/25v Capacitor
3 resistors ( don't know the value????)
1 Pot (don't know the value???)
----------------------------
audio if you think i should add anything to this order that i might need to change or adjust please let me know i would like to order this stuff so i can start to make it and experiment to see how things work... along the way i can be corected, i will post what happens. I figure if i see it i will have a better understanding of this ramp generator work since this is my first eletronic project.
also the values of the resistors that i don't know if your not sure either just tell me what different values i should order....
thanks
max

Maxer

another IC55 schematic that migh work my friend made...
this might require you to change up the LM3914 diagram

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audioguru

Hi Max,
Sorry for my delay.
I don't like the way your new diode pulls down the 555's pin 5 so low that the flip-flop inside the 555 may "latch" and not be able to be triggered by pin 2.

To avoid the problem of a delay on the 1st cycle of the 555, I have been thinking to leave the 555 and the current source transistor powered whenever the bike is running, with pins 2 + 6 and the cap held at a voltage just a little lower than pin2's threshold voltage. When you activate a turn signal switch, the LM3914 will be powered and immediately indicate the 1st LED. At the same time, the voltage limiter on the cap will be released and it ramps normally along with the other LEDs.

I will sketch a "voltage limiter" and the resistors for the current source soon.

magno_grail

Sorry, if I am jumping in late, but it appears you are going about this the hard way. I am presuming you want the LEDs to sequentially turn on, extinguish, then repeat with a constant interval inbetween LED switching?
You need a linear sawtooth generator which can be done on a 555 or OP amp. An OP amp might be more linear over charging with a constant current transistor.
The 3914 only has to measure the voltage of the sawtooth. By adjusting the HI/LO ends of the divider relative to the sawtooth you can have as many or few LED's in the bank up to 100, I believe. The NS data sheet shows examples of stacking the 3914's.
You can keep the discharge time down by using a small capacitance and large charge resistor.
The 3914 is somewhat tricky to set up. I used a 3915 for a programmable ignition. Instead of LEDs I had a bank of resistors discharging the timing capacitor with the 3915 signal input being the capacitor voltage. Very sensitive to the voltage divider HI/LO inputs and the internal reference supply. The LED current is determined by the current drawn from the reference supply (1.2V). You do not have to use that to power the voltage divider. You could actually hook it up across the 555 divider but there will be interaction between the two. The 3914 is around 1k/step and the 555 about 5k between sense and trigger (2&6).
I do not get the reason for the switch on the mode input. For dot mode I believe it is left open and bar mode it connects to the second highest LED cathode through a 10k resistor. Check the National data sheet.

audioguru

Hi Magno,
That's right, we're using a 555 as a linear sawtooth generator with a transistor current source charging its cap. We could have used your opamp idea but the 555 does the same and has the "extra to your circuit" comparator built-in.
An advantage that your opamp idea would have is that its low-point comparator could have a very low voltage threshold (if the opamp is a type that can operate wth its inputs and outputs near its negative supply voltage). This low threshold will minimize the extra long 1st cycle of the sawtooth generator. Unfortunately, a 555 is not designed to have its pin 2 threshold voltage directly changed nor very low.
It is not possible to connect the LM3914's resistor divider between the 555's resistors because pins 2 and 6 of a 555 are the control pins and the resistors are on the opposite side of a differential circuit as reference voltages, so the resistors for pin 2's threshold voltage are not available.
We are operating the LM3914's mode pin correctly. Your connection applied to your cascaded ICs.

magno_grail

I had to take another look at the 555 internal connections. The 2&6 pins are comparitors to the 1/3 and 2/3 Vcc voltage divider. Pin 5 is the direct connection to 2/3 Vcc. There is no external connection to 1/3 Vcc.
The sawtooth will run between 1/3 and 2/3 Vcc. You could connect the HI end of the 3914 to 555 pin 5 then adjust the LO end to get the range you need for the number of LEDs and correct for the discharge cycle time.