0Hz - 600Hz 5v Square Wave Doubler circuit? - Page 1
Forum section: electronics / beginners

author: madhushankarox
author_rank: Newbie
timestamp: March 30, 2015, 08:34:35 am
content: I'm new to this forum and this is my 1st post to ask some help from electronic expertsFirst of all I'm not an Electronic expert or I don't have knowledge to design electronic circuits.Can some one help me to build a square wave doubler circuit to multiply the frequency of a variable square wave? I have an electronic speedometer to be calibrated, so the issue is my speedometer reads 50% off from the actual speed (due to a incompatible sensor).Sensor output is a 5v square wave.Frequency will be 0Hz to 600Hz (169.9Hz = 60Km/h)Here is the speedometer's PCB:(I have tried JayCar speedometer calibration unit too. It was failed to detect the input signal)

author: Rerouter
author_rank: Super Contributor
timestamp: March 30, 2015, 10:08:55 am
content: your driving it with the wrong signal type... 5096 pulses per km (85Hz @ 60) is the norm, add a 10uF cap in series with your input signal and add a 1K resistor on the circuits side of the cap to ground,also for a yazaki pcb of this age replace all the electro's. when these caps leak and they will, they end up chewing that board to bits

author: madhushankarox
author_rank: Newbie
timestamp: March 30, 2015, 12:08:25 pm
content: Quote from: Rerouter on March 30, 2015, 10:08:55 amHey, Thank you very much for the reply. Please see attached image. There is a 1uf cap in series with the signal input (see marked cap). Is it okay to leave it as it is and add an extra 10uf cap in series?(PS: This is not the original PCB. This is an extra one I used to test. I will change caps too.)

author: madhushankarox
author_rank: Newbie
timestamp: March 30, 2015, 01:00:19 pm
content: Quote from: Rerouter on March 30, 2015, 10:08:55 amI've added a capacitor (c1) and a resistor (r1) as follows. c2 is the stock one I already had.I tried inputting a 169Hz wave and It still reads 60Km/h

author: German_EE
author_rank: Super Contributor
timestamp: March 30, 2015, 03:22:34 pm
content: http://www.mikrocontroller.net/attachment/19388/clock_doubler.pngThe 74HC86 is a quad XOR gate.

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 30, 2015, 03:28:21 pm
content: Quote from: German_EE on March 30, 2015, 03:22:34 pmQuote

author: madhushankarox
author_rank: Newbie
timestamp: March 30, 2015, 03:54:14 pm
content: Quote from: German_EE on March 30, 2015, 03:22:34 pmIs there any way to mod above PCB? or do something as previous members idea

author: grumpydoc
author_rank: Super Contributor
timestamp: March 30, 2015, 10:40:44 pm
content: Quote from: madhushankarox on March 30, 2015, 03:54:14 pmYou would need to change the values of R1and C1, however the circuit only works well for a single input frequency depending on the values of these two components. As you move away from that frequency the output will become progressively more asymmetric - at much lower frequencies than intended it will consist of a series of short pulses around the transitions in the input where the pulse duration is a function of the R1C1time constant. As you increase the input frequency the circuit will stop working properly at all once the input frequency is more than twice the set frequency.Your problem is that you actually have quite a wide frequency range to deal with - if you set the values to double the 600Hz output it probably isn't going to work as intended at 1Hz or 10Hz

author: madhushankarox
author_rank: Newbie
timestamp: March 31, 2015, 12:29:51 am
content: Quote from: grumpydoc on March 30, 2015, 10:40:44 pmThank you very much for the reply.. Is there any way to make some changes to the original PCB?

author: grumpydoc
author_rank: Super Contributor
timestamp: March 31, 2015, 06:26:31 am
content: QuoteJust to be clear I was talking about that little clock doubler circuit that was posted.As to the speedo PCB - sometimes there's a resistor which sets the scaling.How have you ended up with an incompatible sensor and speedometer PCB?

author: Sirius631
author_rank: Contributor
timestamp: March 31, 2015, 11:00:19 am
content: Quote from: PA0PBZ on March 30, 2015, 03:28:21 pmI can't go into figures, but it might be possible to make the résistance frequency dependant so that the duty cycle of the output can be maintained at varying frequencies.Place a JFET, drain to source, in series with a smaller resistor, to replace the one currently shown. Take the original square wave, smooth it and apply resultant DC signal to gate of JFET. You'll probably need op-amp to invert or otherwise match JFET's RDS to required frequency response.

author: Ian.M
author_rank: Super Contributor
timestamp: March 31, 2015, 11:14:03 am
content: The first thing I'd check is if the speedo actually needs a reasonably good squarewave, or whether its happy with a low duty cycle pulse as you *may* be over-complicating this.

author: dannyf
author_rank: Super Contributor
timestamp: March 31, 2015, 11:23:09 am
content: Use the frequency signal to drive a motor and on the motor mount a set of sensors, depending on how fast you want to the output signal to be.

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 31, 2015, 11:26:24 am
content: It would be hard to do with discrete logic, but even the smallest pic processor should be good enough to measure the input frequency and output double that.

author: grumpydoc
author_rank: Super Contributor
timestamp: March 31, 2015, 12:25:42 pm
content: QuoteTo do it with a purely digital solution might be quite difficult - totally over-engineering the problem I though you could do it by counting a higher frequency using the input as a gate, then dividing the count by 2 and using that as the input to a programmable divide-by-n counter.Or, presumably, in the analogue doman a suitably configured LM331 acting as a frequency-t-voltage converter could then drive one configured as a voltage-to-frequency converterSledgehammer, nut