# burst generator using a single 556 timer and no external transistor

#### davidjohnhills

Joined Oct 8, 2017
61
Good Evening
is it possible to make a burst generator using a single 556 timer and no external transistor?
I want to create a pulse once a second of duration 0.1 millisecond(15 cycles of 150 khz signal) consisting of 150khz signal
ie a 0.1 millisecond chirp of 150khz once a second

thanks all
David

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#### djsfantasi

Joined Apr 11, 2010
9,131
Good Evening
is it possible to make a chirp generator using a single 556 timer and no external transistor?
I want to create a pulse once a second of duration 0.1 millisecond(15 cycles of 150 khz signal) consisting of 150khz signal
ie a 0.1 millisecond chirp of 150khz once a second

thanks all
David
What will the desired circuit’s output be connected to? A speaker? Another circuit? An IR LED?

The first 555 in the 556 would be used to generate a 1Hz signal with a 0.0001 duty cycle (if that could be accomplished). The 1Hz with that small a duty cycle might be the problem. Then the second 555 would be gated by this signal and configured for 150kHz.

Otherwise, you’ll need different circuitry.

#### crutschow

Joined Mar 14, 2008
33,379
Do you care if the 150kHz signal is truncated or does it need to be a complete set of cycles?

How close to 15 cycles do you need?

You could use a 4-bit digital counter to give exactly 15 cycles with no pulse truncation.

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#### davidjohnhills

Joined Oct 8, 2017
61
What will the desired circuit’s output be connected to? A speaker? Another circuit? An IR LED?

The first 555 in the 556 would be used to generate a 1Hz signal with a 0.0001 duty cycle (if that could be accomplished). The 1Hz with that small a duty cycle might be the problem. Then the second 555 would be gated by this signal and configured for 150kHz.

Otherwise, you’ll need different circuitry.

the output will go to a 150khz amplifier circuit to drive a echo sounder transducer(somehow)
I don't think it matters if the output from the second 555 is truncated It just need to stimulate the base of a RF low frequency amp. I have some 150khz pulse transformers purpose built for transducer matching.

could I invert the duty cycle of the first 555 so its .9999 instead of 0.0001 then invert it, using some passive components(somehow) to drive the reset pin 10 of the second 555(the second 555 pin 10 Reset active low, normally low(disabling output) by pull down to gnd resistor)

I don't think the duration of the second 555 is critical some thing around 7 to 30 cycles at 150Khz
(0.5 TO 20 millsecs)

is chirp generator the right terminology for what I am trying to build?(with the 556)

thanks again
David

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#### davidjohnhills

Joined Oct 8, 2017
61
Hi Eric

I am trying to build a super simple marine echo sounder.

Starting of with separate transducers for transmit and receive. and oscilloscope to measure time difference.

First job is build Transmitter using 556 to burst, LFRF amplifier(impedance match and power), LC Tank(up the voltage), pulse transformer(impedance match), and the transducer .

I have bought some 150khz pulse transformers.(designed for 150khz transducers)
Not sure about the LC tank, think if it high Q it can up the voltage.
(I know the resonate frequency is 1 divided by 2*PI(sqrt(LC)) but there is a infinite combination of L and C that solve this, never sure what pair to use(I believe it's a Q factor thing))

LFRF amp simple common collector configuration for current gain(not sure if this is good upping the output power)NPN

I guess I want peak burst 30volts and duration 10 to 20 cycles at 150khz

Any help much appreciated

David

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#### ericgibbs

Joined Jan 29, 2010
18,288
Hi David,
What range of depths do you want to cover, ie: min and max.?
What Power output in Watts are you aiming for.?

E

jjw

#### Alec_t

Joined Sep 17, 2013
14,014
is chirp generator the right terminology for what I am trying to build?
'Burst' would be more appropriate? 'Chirp' denotes a swept frequency, which probably isn't what you want.

#### crutschow

Joined Mar 14, 2008
33,379

#### davidjohnhills

Joined Oct 8, 2017
61
Hi David,
What range of depths do you want to cover, ie: min and max.?
What Power output in Watts are you aiming for.?

E
depth up to 100 meters
power not sure, a few watts maybe, i'll tale a look at the transducer spec and get back to you

#### davidjohnhills

Joined Oct 8, 2017
61
'Burst' would be more appropriate? 'Chirp' denotes a swept frequency, which probably isn't what you want.
Thanks I'll edit the post

#### davidjohnhills

Joined Oct 8, 2017
61

#### davidjohnhills

Joined Oct 8, 2017
61
depth up to 100 meters
power not sure, a few watts maybe, i'll tale a look at the transducer spec and get back to you

Nasa 150Khz Depth Transducer
Replacement depth transducer with 7m of cable.
• Supply voltage: 12V DC
• Power consumption: nominal 120mA
• Power output: 100w + pulse
• Operating frequency: nominal 150kHz
• Dimensions: Length Overall: 106mm, Face Dia: 38mm, Thread Dia: 16mm
Suitable for use with Nasa Clipper, Target & Stingray instruments.
For In-Hull mounting kit see product code: 220035, for Thru-Hull mounting kit see product code: 220048

#### davidjohnhills

Joined Oct 8, 2017
61
hi David,
My Blog entry is an example of what you are asking, the R/C components will have to be adjusted to give 150kHz.
For ultrasonic drive, I would recommend 50:50 mark/space ratio on the 150kHz
What is the application.?
E
Yes the 2 555's look like there doing exactly what I need , slight issue trying to produce a duty cycle of 0.0001, thought about .9999 duty cycle and inverting it before apply to 2nd 555 reset pin.

#### ericgibbs

Joined Jan 29, 2010
18,288
produce a duty cycle of 0.0001, thought about .9999 duty cycle and inverting it before apply to 2nd 555 reset pin.
Hi David,
The way I read this, you want to Gate On the 150kHz pulse gen from 0.1mSec [15 cycles] to 1mSec [150 cycles] .??
Be aware that the transducer will take 2 to 4 pulses before it goes resonant at full power.

E

#### davidjohnhills

Joined Oct 8, 2017
61
Hi David,
The way I read this, you want to Gate On the 150kHz pulse gen from 0.1mSec [15 cycles] to 1mSec [150 cycles] .??
Be aware that the transducer will take 2 to 4 pulses before it goes resonant at full power.

E
Not quite sure I understand (do you mean window by 'Gate on'), I want a 1 millisecond pulse(window) of 150khz(that about 15 cycles) once a second. I don't know if 15 cycles is the right amount, but the output from my old analogue Seafarer 501 look like about 10 to 15 cycles on my scope.

thanks for taking the time to reply

#### crutschow

Joined Mar 14, 2008
33,379
Below is the LTspice simulation of a gated burst using two 555 (or one 556) timer(s), but I couldn't avoid an external transistor.
By adding an emitter follower buffer (Q1) to rapidly charge C2, the circuit was able to generate the short 0.1ms output pulse (as determined by R2) with a 1s period (as determined by R1).
The U2 astable generates the 150kHz signal.
R5 allows adjusting the duty-cycle to give an approximate 50% duty-cycle output.

As you can see, the 150kHz burst from U2 is 16 cycles long.

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#### eetech00

Joined Jun 8, 2013
3,679
Not quite sure I understand (do you mean window by 'Gate on'), I want a 1 millisecond pulse(window) of 150khz(that about 15 cycles) once a second. I don't know if 15 cycles is the right amount, but the output from my old analogue Seafarer 501 look like about 10 to 15 cycles on my scope.

thanks for taking the time to reply

You have a transducer that operates at 150Khz.
You want a pulse generator that will turn on the transducer for 1ms every 1s
You want to be able to enable/disable the pulse generator.
You would like to use a 555 timer(s) if possible.

Is this correct?

How much drift/accuracy is required for the timing?
A 555(s) may not be a good choice...

maybe a CD4040B with crystal time base.

#### davidjohnhills

Joined Oct 8, 2017
61

You have a transducer that operates at 150Khz.
You want a pulse generator that will turn on the transducer for 1ms every 1s
You want to be able to enable/disable the pulse generator.
You would like to use a 555 timer(s) if possible.

Is this correct?

How much drift/accuracy is required for the timing?
A 555(s) may not be a good choice...

maybe a CD4040B with crystal time base.
555 is in my comfort zone at my present level of knowledge,just to get started on this

#### davidjohnhills

Joined Oct 8, 2017
61
Below is the LTspice simulation of a gated burst using two 555 (or one 556) timer(s), but I couldn't avoid an external transistor.
By adding an emitter follower buffer (Q1) to rapidly charge C2, the circuit was able to generate the short 0.1ms output pulse (as determined by R2) with a 1s period (as determined by R1).
The U2 astable generates the 150kHz signal.
R5 allows adjusting the duty-cycle to give an approximate 50% duty-cycle output.

As you can see, the 150kHz burst from U2 is 16 cycles long.

View attachment 258787
Great , I have all these parts, I have a go building it with the 2 555,
I'll post the actual timing vales for c and r once its work
thanjs