ac sine to dc square

Ok so basically i search the internet found a basic schematic remade/ changed the schematic a little in DipTrace. my Speedometer Requires a dc square wave between 5 and 14 volts but the 2 wire sensor sends out an ac sine wave not sure of the voltage. i built the board tested it with an oscilloscope ac sine in dc square out no problem. now when i hook my speedometer up to it, it completly loses the square wave. can someone look at the schematic and tell me what i did wrong? plz and thank you. https://dl.dropboxusercontent.com/u/93944822/Sine%20to%20Sqr.dch Note: it is a Diptrace file.

I can't open the file, but what does the output state consist of? It sounds like you are loading the output beyond its capabilities. Kevin Pierson

I couldn't open it using fileView. Maybe upload a (scaled) screenshot of the circuit instead?

ok screen cap. https://dl.dropboxusercontent.com/u/93944822/Sine%20to%20Sqr.png Sorry about that.

The next question is how much current does your speedo require to move the needed? What year is this vehicle? Does the speedo have a sending unit or are you driving it directly? Your circuit, with an op amp outputting through a 1K resistor is going to be extremely limited in current (at 5vdc you'll have no more then 5mA of current). If you attempt to load the output past 5mA your voltage will drop until the signal is completely gone.Kevin Pierson

If it is a true square wave you should be able to add a transistor directly to the output. If your duty cycle is not 50% you may need to add two transistors as a single transistor will inverse your output.Kevin Pierson

POST EDIT - Dang! I've essentially duplicated KP's replies above. Akin to KP, I'd suggest the transistor circuit in my 3rd link below. /end POST EDIT It looks to be a very high impedance circuit - ie, 1k in series with the supply (suggesting maybe a max of maybe 5mA for the circuit) but more so the 1K output resistor. It is quite possible your speedo has an input impedance of a few hundred Ohms, hence the 1k output resistor is being "swamped". You could try bypassing the output 1k resistor else using the unused opamp as a buffer (voltage follower - inverting of non inverting) assuming the OpAmp can supply the required current (impedance). I was expecting a simpler circuit - maybe even mere passives if the slope isn't too important - but otherwise using Schmitts etc - eg, seekic's Sine wave-square wave converter circuit or tradeofic's Sine wave to square wave converter or edaboard's How to convert Sinewave to sqr wave from ADC samples?. If using chips as per the first 2 lnks, I'd suggest an open collector output output(as opposed to the 4093), but I can only find open collector NAND gates etc. But having the 4093 drive a transistor or FET achieves the same (ie, open collector or open drain). You merely need to know what current is required and if the speedo has its own pull-up resistor (it should; I'd expect merely a grounding signal is required).

KPierson wrote: The next question is how much current does your speedo require to move the needed? What year is this vehicle? Does the speedo have a sending unit or are you driving it directly? Your circuit, with an op amp outputting through a 1K resistor is going to be extremely limited in current (at 5vdc you'll have no more then 5mA of current). If you attempt to load the output past 5mA your voltage will drop until the signal is completely gone.

its a variable reluctance sender in a 700r4. The speedometer is a digital speedometer i bought from intellitronix. There tech support told me it requires a 5-14v square wave. From my research the sender on the 700r4 sends out sine wave. i haven't actually hooked it to the transmission yet i used a function generator to simulate the sine wave and used an oscilloscope to watch the output. as soon as i hooked the speedometer to it the signal went from a nice 50/50 (or close to it) square to nothing. would a transistor work in this case?

If it's a reluctor then it's a distorted sinewave. Not that that should matter, though I was originally thinking of suggesting an ignitor from a reluctor type car ignition. But reluctor output voltage varies with speed and that could be a complication. As to "variable reluctance" I amn't sure - I'd have to look that up (maybe it's a saturated pickup coil or similar?), but that will have to wait. The tech's 5-14V info says nothing about the current required, but yes, IMO a transistor or FET added to your circuit should work - merely an N-type with emitter or source to GND, and collector or drain "open" - ie, to the speedo with a resistor to the speedo's +12V else IGN +12V if the speedo does not have its own pull-up resistor. Maybe the techs can answer if the speedo takes an open collector output, but I'd assume it does due to its 5-14V requirements. The might also know if an external pullup (resistor) us required.

Ok, so variable reluctance simply means a reluctor type system. There are 700r4 senders that have digital outputs. Though their pulses-per-distance vary from the reluctor type, that should not be an issue for modern electronic speedo kits which can be calibrated to a wide range of gearing and pulse counts.