Hello all,
I am trying to create a circuit that will only be "hot" when the engine is running.
I believe the LM2917-8 will work for my purposes but I am having a difficult time getting it to work. I've tried using the schematics in the datasheet. Specifically Figure 18 "Speed Switch," Figure 19 "Zener Regulated Frequency to Voltage Converter" & Figure 32 "Over-Speed Latch Circuit Diagram."
http://www.ti.com/lit/ds/symlink/lm2917-n.pdf
I calculated that Pin 2 should use .22uF CAP and Pin 3 should be 68k w/1uF CAP. That combination didn't work so I reverted back to the data sheet and used the numbers from Figure 19 which are .02uF for C1, 100k for R1 & C2 at 1uF.
Figure 18 didn't work at all.
Figure 19 did work for me, but the chip got really hot, and I was using the 470 resistor on Pin 6. It was also drawing quite a bit of current (over 200mA). I wasn't able to test if frequency going to 0Hz shut this circuit down since I shut the circuit down before anything started to melt.
Figure 32 would only work if I removed the 5k resistor between 7 & 8 and replaced it with a jumper wire. When I did that I was able to get a Vo to activate an LED (using this for test purposes) but the only way to shut off the circuit was by removing Vcc. I need the output to go to 0v when frequency drops below 40Hz, if that is even possible.
Here's what I have to work with:
12v constant power supplied by Body Control Module
"Clean Tach Out" signal from PCM - 4 pulses per engine revolution. I measured 40Hz @ 600 RPM (Idle) to 200Hz @ 3000 RPM. Voltage ranged from 6.69v to 7.14v and duty cycle was at 50%. The higher the RPM the lower the voltage. I do not have a scope and was using a Multimeter to measure the output. This is a diesel pickup so it's a "simulated" tach signal that uses the alternator to determine RPM.
The output from the LM2917 will be used to send power via transistor (preferred) or relay, to a delay-on circuit which triggers a relay to send 12v to the high idle circuit in the Body Control Module. Yes, I could use a key-on circuit and eliminate the need for the F-V circuit but the high idle will not activate with my factory remote start system if I go that route. Plus all the wires I need are right under the steering column with easy access and I've always wanted to learn more about IC's.
I presume it's the resistor/cap combos that are not correct and/or the digital pulse signal that I am trying to use. I don't understand what I need to adjust or how my adjustments affect the circuit. This is the first time I've played around with IC's and I am trying to learn. I would rather avoid guessing and burning up components as well.
Any help is greatly appreciated
I am trying to create a circuit that will only be "hot" when the engine is running.
I believe the LM2917-8 will work for my purposes but I am having a difficult time getting it to work. I've tried using the schematics in the datasheet. Specifically Figure 18 "Speed Switch," Figure 19 "Zener Regulated Frequency to Voltage Converter" & Figure 32 "Over-Speed Latch Circuit Diagram."
http://www.ti.com/lit/ds/symlink/lm2917-n.pdf
I calculated that Pin 2 should use .22uF CAP and Pin 3 should be 68k w/1uF CAP. That combination didn't work so I reverted back to the data sheet and used the numbers from Figure 19 which are .02uF for C1, 100k for R1 & C2 at 1uF.
Figure 18 didn't work at all.
Figure 19 did work for me, but the chip got really hot, and I was using the 470 resistor on Pin 6. It was also drawing quite a bit of current (over 200mA). I wasn't able to test if frequency going to 0Hz shut this circuit down since I shut the circuit down before anything started to melt.
Figure 32 would only work if I removed the 5k resistor between 7 & 8 and replaced it with a jumper wire. When I did that I was able to get a Vo to activate an LED (using this for test purposes) but the only way to shut off the circuit was by removing Vcc. I need the output to go to 0v when frequency drops below 40Hz, if that is even possible.
Here's what I have to work with:
12v constant power supplied by Body Control Module
"Clean Tach Out" signal from PCM - 4 pulses per engine revolution. I measured 40Hz @ 600 RPM (Idle) to 200Hz @ 3000 RPM. Voltage ranged from 6.69v to 7.14v and duty cycle was at 50%. The higher the RPM the lower the voltage. I do not have a scope and was using a Multimeter to measure the output. This is a diesel pickup so it's a "simulated" tach signal that uses the alternator to determine RPM.
The output from the LM2917 will be used to send power via transistor (preferred) or relay, to a delay-on circuit which triggers a relay to send 12v to the high idle circuit in the Body Control Module. Yes, I could use a key-on circuit and eliminate the need for the F-V circuit but the high idle will not activate with my factory remote start system if I go that route. Plus all the wires I need are right under the steering column with easy access and I've always wanted to learn more about IC's.
I presume it's the resistor/cap combos that are not correct and/or the digital pulse signal that I am trying to use. I don't understand what I need to adjust or how my adjustments affect the circuit. This is the first time I've played around with IC's and I am trying to learn. I would rather avoid guessing and burning up components as well.
Any help is greatly appreciated