Looking for a fish finder schematic

Thread Starter

BigAl12

Joined Jan 14, 2022
8
Hi All, I'm looking for a schematic for an old style fishing flasher with a rotating disc display. Something like a Lowrance Fish Lo-k-tor, Humminbird bird trap or Heathkit Depthsounder.

Thanks
 

SamR

Joined Mar 19, 2019
4,127
Welcome to AAC!

Good luck. Most of the US fish finder makers starting back in the 70-80s would not publish their schematics because at that time the Japanese would build copies from them and ruin their international sales. A buddy was able to obtain one by calling the factory and explaining it was for his own personal use. Not sure what the current situation is but a quick search on the net did not find anything for me other than installation and operation manuals and diagrams.
 

ericgibbs

Joined Jan 29, 2010
15,349
hi Al,
Get a LM1812 IC, a bit dated, but they form the basis of a simple sounder.
The display can be a rotating arm, with slip rings, driving LEDs at the zero depth and target depth.
Use a 150kHz yacht sounder transducer.
E
 

Attachments

SamR

Joined Mar 19, 2019
4,127
I have to ask the question. Why? I've used fish finders for over 50 years and never really liked flashers. A relative had a very expensive commercial marine Raytheon unit on his shrimp trawler that plotted out on tractor drive paper (no monitors back then). It wasn't even turned on after the first couple of months. That was 1950-60s technology and has been vastly improved upon. Better use would have been as an anchor which is why I threw my 6" color CRT unit away a year after buying that expensive relic in the 90s. The latest chirp technology finally gives a bit of bottom resolution in the 50-70' waters I fish in offshore. For some reason even the new digital units still have a flasher mode for the die-hards.
 

Thread Starter

BigAl12

Joined Jan 14, 2022
8
Good question. Believe it or not the newer model flashers are still quite popular for ice fishing, but I have to write a paper for my electronics class in trade school. The topic I chose was the ice fishing flasher. I was hoping to get a schematic of the early ones to see how they functioned at the most basic level.
 

debe

Joined Sep 21, 2010
1,294
Heres a few to check out. I do have a few others that are paper sounder circuits. The FE-300 uses the LM1812 IC & in this circuit is 200Khz, i still have one of these Ics. The Fuso MF25A is a basic just disc type, & i still have it. Could take pictures of it & its insides if its any help.FURUNO FE300.1.jpgFUSO MF_25A.6.jpgFUSO MF_25A.7.jpgMARLIN MR360.1.jpgMARLIN MR360.2.jpg
 
Last edited:

Thread Starter

BigAl12

Joined Jan 14, 2022
8
hi Al12,
Does this edited circuit help you understand the receiver section.?
Ask if you have a query.
E
Thanks, that certainly helps.
I think the page with the timer was included accidentally. I still do have a few questions regarding this circuit.
Is the frequency of the pulse determined when the magnet passes the pick up coil? Or is there any component in this circuit that can increase the frequency?
Does the 200kHz tuned amplifier use a capacitor and the transformer as a bandpass filter to only allow a 200kHz pulse to reach the 2 stage amplifier?
What is the function of the pulse width discriminator?
 

ericgibbs

Joined Jan 29, 2010
15,349
Hi Al,
Is the frequency of the pulse determined when the magnet passes the pick up coil?
Or is there any component in this circuit that can increase the frequency?


L2 is a auto transformer winding, of the transformer, it is tuned to a resonant frequency of 200kHz, which is the frequency required by the transducer.
---------
Does the 200kHz tuned amplifier use a capacitor and the transformer as a bandpass filter to only allow a 200kHz pulse to reach the 2 stage amplifier?

Yes, T1 , is a transformer tuned for a 200kHz bandpass response, so that Q9 will provide a maximum gain signal gain for frequencies at ~200kHz.
So the two AC untuned amplifier stages will only further amplify the required 200kHz signal

The detector is basically a rectifier and smoothing capacitor, Rc,Ct & Dc, so the PWD input is a ‘DC’ pulse.
------------------
What is the function of the pulse width discriminator?

It designed to only allow through echo pulses with duration’s greater than a fixed period, basically cuts out ‘noise spike’ pulses that could trigger the neon.

This image is a LTspice simulation of a simplified section of the receiver, it may help you understand the receiver operation.
E
Note: the V(trx) trace, shows the initial transmit pulse at time 0.0mSec and simulated Echo pulse at ~4mSec

EG 1404.gif
 
Last edited:

Thread Starter

BigAl12

Joined Jan 14, 2022
8
Hi Al,
Is the frequency of the pulse determined when the magnet passes the pick up coil?
Or is there any component in this circuit that can increase the frequency?


L2 is a auto transformer winding, of the transformer, it is tuned to a resonant frequency of 200kHz, which is the frequency required by the transducer.
---------
Does the 200kHz tuned amplifier use a capacitor and the transformer as a bandpass filter to only allow a 200kHz pulse to reach the 2 stage amplifier?

Yes, T1 , is a transformer tuned for a 200kHz bandpass response, so that Q9 will provide a maximum gain signal gain for frequencies at ~200kHz.
So the two AC untuned amplifier stages will only further amplify the required 200kHz signal

The detector is basically a rectifier and smoothing capacitor, Rc,Ct & Dc, so the PWD input is a ‘DC’ pulse.
------------------
What is the function of the pulse width discriminator?

It designed to only allow through echo pulses with duration’s greater than a fixed period, basically cuts out ‘noise spike’ pulses that could trigger the neon.

This image is a LTspice simulation of a simplified section of the receiver, it may help you understand the receiver operation.
E
Note: the V(trx) trace, shows the initial transmit pulse at time 0.0mSec and simulated Echo pulse at ~4mSec

View attachment 260715
thanks again, this helps out a bundle.
 

Thread Starter

BigAl12

Joined Jan 14, 2022
8
Hi Al,
Is the frequency of the pulse determined when the magnet passes the pick up coil?
Or is there any component in this circuit that can increase the frequency?


L2 is a auto transformer winding, of the transformer, it is tuned to a resonant frequency of 200kHz, which is the frequency required by the transducer.
---------
Does the 200kHz tuned amplifier use a capacitor and the transformer as a bandpass filter to only allow a 200kHz pulse to reach the 2 stage amplifier?

Yes, T1 , is a transformer tuned for a 200kHz bandpass response, so that Q9 will provide a maximum gain signal gain for frequencies at ~200kHz.
So the two AC untuned amplifier stages will only further amplify the required 200kHz signal

The detector is basically a rectifier and smoothing capacitor, Rc,Ct & Dc, so the PWD input is a ‘DC’ pulse.
------------------
What is the function of the pulse width discriminator?

It designed to only allow through echo pulses with duration’s greater than a fixed period, basically cuts out ‘noise spike’ pulses that could trigger the neon.

This image is a LTspice simulation of a simplified section of the receiver, it may help you understand the receiver operation.
E
Note: the V(trx) trace, shows the initial transmit pulse at time 0.0mSec and simulated Echo pulse at ~4mSec

View attachment 260715
I'm still having a bit of trouble wrapping my head around the detector. what is the purpose of of rectifying the pulse at this point? How does T2 transform the DC pulse to almost 270v to power the neon lamp?
 

ericgibbs

Joined Jan 29, 2010
15,349
Hi Al,

The rectifier is required so that the PWD can compare the DC levels at Vd1 and Vd2.

L1 & L2 form a step up transformer of approx 1:22 , so 12V swing on L1 , gives a 22*12V on L2.
The Neon requires about 170V to 'strike' [ flash]

E
EG 1411.gif
 
Last edited:
Top