Multimeters and test equipment.

[mudnut]

The Uni-T 2000 series Benchtop oscilloscope is a bloody marvellous piece of kit. The sig gen I created to run speedos was having interference problems when plugged into 12v. Yet I could only see a nice looking square wave at the 555 timer chip, on the Allosun handheld. I found that having a power lead more than a few centimeters causes the rise on the wave to become fuzzy so I will purchase a small rechargeable 12v battery to install on a new sig gen I am making. I really do recommend the Uni-T as a reasonably priced unit.

[Brissieboy]

The Uni-T 2000 series Benchtop oscilloscope is a bloody marvellous piece of kit. The sig gen I created to run speedos was having interference problems when plugged into 12v. Yet I could only see a nice looking square wave at the 555 timer chip, on the Allosun handheld. I found that having a power lead more than a few centimeters causes the rise on the wave to become fuzzy so I will purchase a small rechargeable 12v battery to install on a new sig gen I am making. I really do recommend the Uni-T as a reasonably priced unit.

Before you bother with the battery idea, try puting a 0.1uF ceramic or vitramon or similar capacitor across the supply rails right at the 555 (pins 1 & 8). And make sure your ground rail is solid and short as possible. Digital circuits need power supply decoupling.

[mudnut]

Before you bother with the battery idea, try puting a 0.1uF ceramic or vitramon or similar capacitor across the supply rails right at the 555 (pins 1 & 8). And make sure your ground rail is solid and short as possible. Digital circuits need power supply decoupling.

I've tried a few ideas as well. Pi filters, common modes chokes, etc. It comes down to the length of the leads. I will try a shielded cable. Also 9v batteries seem to be going flat in no time these days.

[BillsGU]

What ripple frequency was your Pi filter designed to decouple?

[mudnut]

What ripple frequency was your Pi filter designed to decouple?

The 50hz of the power supply I use. I also found placing a small ceramic cap across pins 1 and 8 caused a weird feedback frequency. The best I have so far found is to have a sizable 12 volt gel battery with a an IC7809 to regulate its output. This gives me the option to run a Bd139 as an inverting switch on the 555 output to get a nice AC Square wave. I am now playing with different configurations to get a smooth enough signal at frequencies between 30hz and around440-480hz. I found that around 270hz is 100kph.

[BillsGU]

Have a close look at the ripple frequency. The ripple out of a full wave rectifier is 100hz. The frequency you are trying to generate is close to your filter frequency and you may be getting some feedback via the filters. You could try using an opto coupler to ensure isolation.

Or get one of these: https://www.westlab.com.au/signal-ge...b-0-1hz-100khz

[mudnut]

Have a close look at the ripple frequency. The ripple out of a full wave rectifier is 100hz. The frequency you are trying to generate is close to your filter frequency and you may be getting some feedback via the filters. You could try using an opto coupler to ensure isolation.

Or get one of these: https://www.westlab.com.au/signal-ge...b-0-1hz-100khz

I need the sig gen to be portable, small and robust. So I can disconnect the speed sensor connector and test the wiring harness and cluster.
I've been looking into the interference. I think the configuration of the my 555 is too sensitive to outside influence. It uses a capacitor and around 120-130 kohms between pins 1and 2. I will try a different set up using pots between pins 8,7 and 6.

[mudnut]

Yep. The 555 circuit I picked was just to sensitive. I built another one today which handles 10-18 volts, either 240v fed Power supply or 12 battery with no interference whatsoever.

[BillsGU]

Sometimes starting from scratch is the way to go. Beats chasing your tail and trying to fix problems by introducing more problems. Every extra component you put into a circuit is a potential issue.

[mudnut]

Sometimes starting from scratch is the way to go. Beats chasing your tail and trying to fix problems by introducing more problems. Every extra component you put into a circuit is a potential issue.

Too right.

I was looking to buy a dedicated frequency meter kit online to add to the sig gen. Going to use a cheap Jaycar multimeter and strip it down just to display volts and Hz.